refactor(plugins)!: use OpenTelemetry for BigQuery plugin tracing

This refactors the BigQueryAgentAnalyticsPlugin to use the standard OpenTelemetry API for trace and span ID generation and propagation, replacing the custom ContextVar implementation.

Key changes:
- Utilizes `opentelemetry.trace` for starting/ending spans.
- Correctly uses `opentelemetry.context` for context attachment and detachment.
- Span information is now derived from the OpenTelemetry context when available.
- Added a fallback mechanism to ensure span_id and parent_span_id are still populated if the OpenTelemetry SDK is not initialized.

To get standard OpenTelemetry trace information in BigQuery logs, users should install `opentelemetry-sdk` and initialize a global `TracerProvider` in their application *before* initializing ADK components.

Example minimal initialization:
```python
# Install: pip install opentelemetry-sdk
from opentelemetry import trace
from opentelemetry.sdk.trace import TracerProvider
trace.set_tracer_provider(TracerProvider())
```

PiperOrigin-RevId: 858965562

tests/unittests/plugins/test_bigquery_agent_analytics_plugin.py

@@ -37,6 +37,7 @@ import google.auth.credentials
 from google.cloud import bigquery
 from google.cloud import exceptions as cloud_exceptions
 from google.genai import types
+from opentelemetry import trace
 import pyarrow as pa
 import pytest
 
@@ -502,28 +503,34 @@ class TestBigQueryAgentAnalyticsPlugin:
     bigquery_agent_analytics_plugin.TraceManager.init_trace(callback_context)
 
     async def branch_1():
-      bigquery_agent_analytics_plugin.TraceManager.push_span(
-          callback_context, span_id="span-1"
+      s_id = bigquery_agent_analytics_plugin.TraceManager.push_span(
+          callback_context, span_name="span-1"
       )
       await asyncio.sleep(0.02)
-      s_id = bigquery_agent_analytics_plugin.TraceManager.get_current_span_id()
+      current_s_id = (
+          bigquery_agent_analytics_plugin.TraceManager.get_current_span_id()
+      )
+      assert s_id == current_s_id
       bigquery_agent_analytics_plugin.TraceManager.pop_span()
       return s_id
 
     async def branch_2():
-      bigquery_agent_analytics_plugin.TraceManager.push_span(
-          callback_context, span_id="span-2"
+      s_id = bigquery_agent_analytics_plugin.TraceManager.push_span(
+          callback_context, span_name="span-2"
       )
       await asyncio.sleep(0.02)
-      s_id = bigquery_agent_analytics_plugin.TraceManager.get_current_span_id()
+      current_s_id = (
+          bigquery_agent_analytics_plugin.TraceManager.get_current_span_id()
+      )
+      assert s_id == current_s_id
       bigquery_agent_analytics_plugin.TraceManager.pop_span()
       return s_id
 
     # Run concurrently
     results = await asyncio.gather(branch_1(), branch_2())
     # If they shared the same list/dict, they would interfere.
-    assert "span-1" in results
-    assert "span-2" in results
+    assert results[0] is not None
+    assert results[1] is not None
     assert results[0] != results[1]
 
   @pytest.mark.asyncio
@@ -1953,3 +1960,104 @@ class TestBigQueryAgentAnalyticsPlugin:
     content_json = json.loads(log_entry["content"])
     assert content_json["result"]["id"] == "inc-123"
     assert content_json["result"]["kpi_missed"][0]["kpi"] == "latency"
+
+  @pytest.mark.asyncio
+  async def test_otel_integration(
+      self,
+      callback_context,
+  ):
+    """Verifies OpenTelemetry integration in TraceManager."""
+    # Mock the tracer and span
+    mock_tracer = mock.Mock()
+    mock_span = mock.Mock()
+    mock_context = mock.Mock()
+
+    # Setup mock IDs (128-bit trace_id, 64-bit span_id)
+    trace_id_int = 0x12345678123456781234567812345678
+    span_id_int = 0x1234567812345678
+
+    mock_context.trace_id = trace_id_int
+    mock_context.span_id = span_id_int
+    mock_context.is_valid = True
+
+    mock_span.get_span_context.return_value = mock_context
+    mock_span.start_time = 1234567890000000000  # Mock start time in ns
+    mock_tracer.start_span.return_value = mock_span
+
+    # Patch the global tracer in the plugin module
+    with mock.patch(
+        "google.adk.plugins.bigquery_agent_analytics_plugin.tracer", mock_tracer
+    ):
+      # Test push_span
+      span_id = bigquery_agent_analytics_plugin.TraceManager.push_span(
+          callback_context, "test_span"
+      )
+
+      mock_tracer.start_span.assert_called_with("test_span")
+      assert span_id == format(span_id_int, "016x")
+
+      # Test get_trace_id
+      # We need to mock trace.get_current_span() to return our mock span
+      # because push_span calls trace.attach(), which affects the global context
+      with mock.patch(
+          "opentelemetry.trace.get_current_span", return_value=mock_span
+      ):
+        trace_id = bigquery_agent_analytics_plugin.TraceManager.get_trace_id(
+            callback_context
+        )
+        assert trace_id == format(trace_id_int, "032x")
+
+      # Test pop_span
+      # pop_span calls span.end()
+      bigquery_agent_analytics_plugin.TraceManager.pop_span()
+      mock_span.end.assert_called_once()
+
+  @pytest.mark.asyncio
+  async def test_otel_integration_real_provider(self, callback_context):
+    """Verifies TraceManager with a real OpenTelemetry TracerProvider."""
+    # Setup OTEL with in-memory exporter
+    # pylint: disable=g-import-not-at-top
+    from opentelemetry.sdk import trace as trace_sdk
+    from opentelemetry.sdk.trace import export as trace_export
+    from opentelemetry.sdk.trace.export import in_memory_span_exporter
+
+    # pylint: enable=g-import-not-at-top
+
+    provider = trace_sdk.TracerProvider()
+    exporter = in_memory_span_exporter.InMemorySpanExporter()
+    processor = trace_export.SimpleSpanProcessor(exporter)
+    provider.add_span_processor(processor)
+    tracer = provider.get_tracer("test_tracer")
+
+    # Patch the global tracer in the plugin module
+    with mock.patch(
+        "google.adk.plugins.bigquery_agent_analytics_plugin.tracer", tracer
+    ):
+      # 1. Start a span
+      span_id = bigquery_agent_analytics_plugin.TraceManager.push_span(
+          callback_context, "test_span"
+      )
+
+      # Verify a span was started but not ended
+      current_spans = exporter.get_finished_spans()
+      assert not current_spans
+
+      # Verify we can retrieve the trace ID
+      trace_id = bigquery_agent_analytics_plugin.TraceManager.get_trace_id(
+          callback_context
+      )
+      assert trace_id is not None
+
+      # 2. End the span
+      popped_span_id, _ = (
+          bigquery_agent_analytics_plugin.TraceManager.pop_span()
+      )
+
+      assert popped_span_id == span_id
+
+      # Verify span is now finished and exported
+      finished_spans = exporter.get_finished_spans()
+      assert len(finished_spans) == 1
+      assert finished_spans[0].name == "test_span"
+      assert format(finished_spans[0].context.span_id, "016x") == span_id
+      assert format(finished_spans[0].context.trace_id, "032x") == trace_id