docs: fixing typo in multiple files

Merge https://github.com/google/adk-python/pull/3944

### Link to Issue or Description of Change

**1. Link to an existing issue (if applicable):** N/A

**2. Or, if no issue exists, describe the change:** fixing various typos in multiple files: see commit diffs for details

**Problem:**

Discovered typos while reading ADK repo

**Solution:**

Submitted this PR to fix them

### Testing Plan

N/A: changes only in comments, .md and docstrings.

**Unit Tests:**

- [N/A ] I have added or updated unit tests for my change.
- [X] All unit tests pass locally.

_Please include a summary of passed `pytest` results._

**Manual End-to-End (E2E) Tests:**

N/A

### Checklist

- [X] I have read the [CONTRIBUTING.md](https://github.com/google/adk-python/blob/main/CONTRIBUTING.md) document.
- [X] I have performed a self-review of my own code.
- [N/A] I have commented my code, particularly in hard-to-understand areas.
- [N/A] I have added tests that prove my fix is effective or that my feature works.
- [X] New and existing unit tests pass locally with my changes.
- [N/A] I have manually tested my changes end-to-end.
- [N/A] Any dependent changes have been merged and published in downstream modules.

### Additional context

N/A

COPYBARA_INTEGRATE_REVIEW=https://github.com/google/adk-python/pull/3944 from didier-durand:fix-typos-a 02378a488d9a87ac9b6b7397fe9ad7c393faf16a
PiperOrigin-RevId: 868245940

src/google/adk/agents/llm_agent.py

@@ -469,7 +469,7 @@ class LlmAgent(BaseAgent):
         self.__maybe_save_output_to_state(event)
         yield event
         if ctx.should_pause_invocation(event):
-          # Do not pause immediately, wait until the long running tool call is
+          # Do not pause immediately, wait until the long-running tool call is
           # executed.
           should_pause = True
     if should_pause:
@@ -479,7 +479,7 @@ class LlmAgent(BaseAgent):
       events = ctx._get_events(current_invocation=True, current_branch=True)
       if events and any(ctx.should_pause_invocation(e) for e in events[-2:]):
         return
-      # Only yield an end state if the last event is no longer a long running
+      # Only yield an end state if the last event is no longer a long-running
       # tool call.
       ctx.set_agent_state(self.name, end_of_agent=True)
       yield self._create_agent_state_event(ctx)

src/google/adk/models/gemini_llm_connection.py

@@ -142,7 +142,7 @@ class GeminiLlmConnection(BaseLlmConnection):
   def __build_full_text_response(self, text: str):
     """Builds a full text response.
 
-    The text should not partial and the returned LlmResponse is not be
+    The text should not be partial and the returned LlmResponse is not
     partial.
 
     Args:

src/google/adk/models/gemma_llm.py

@@ -323,7 +323,7 @@ def _get_last_valid_json_substring(text: str) -> tuple[bool, str | None]:
   """Attempts to find and return the last valid JSON object in a string.
 
   This function is designed to extract JSON that might be embedded in a larger
-  text, potentially with introductory or concluding remarks. It will always chose
+  text, potentially with introductory or concluding remarks. It will always choose
   the last block of valid json found within the supplied text (if it exists).
 
   Args:

src/google/adk/tools/openapi_tool/openapi_spec_parser/tool_auth_handler.py

@@ -321,7 +321,7 @@ class ToolAuthHandler:
     credential = existing_credential or self.auth_credential
     # fetch credential from adk framework
     # Some auth scheme like OAuth2 AuthCode & OpenIDConnect may require
-    # multi-step exchange:
+    # multistep exchange:
     # client_id , client_secret -> auth_uri -> auth_code -> access_token
     # adk framework supports exchange access_token already
     # for other credential, adk can also get back the credential directly