Merge https://github.com/google/adk-python/pull/1079
Fixes part of #356
Add usage attributes to span.
Note: Since the handling of GenAI event bodies in OpenTelemetry has not yet been determined, I have temporarily added only attributes related to usage.
COPYBARA_INTEGRATE_REVIEW=https://github.com/google/adk-python/pull/1079 from soundTricker:feature/356-support-more-opentelemetry-semantics 99a9d0352b4bca165baa645440e39ce7199f072b
PiperOrigin-RevId: 774834279