fix: Fixing tracing for function calls

[copybara-service]

fix: Fixing tracing for function calls

Fixing when the execute tool happens in the graph. Refactor and simplify the tracing logic for function and tool calls within the ADK. The primary goal is to consolidate multiple tracing events into more cohesive operations, specifically merging "tool_call" and "tool_response" into a single "execute_tool" operation.

Key Changes:

• Consolidated Tool Tracing: Replaced the separate traceToolCall and traceToolResponse methods with a unified traceToolExecution in Tracing.java. This reduces span noise by representing a tool's lifecycle as a single "execute_tool" operation containing both arguments and results (or errors).
• Standardized Operation Names: Introduced constants for core Gen AI operations: invoke_agent, execute_tool, send_data, and call_llm.
• Improved Error Tracing: traceToolExecution and traceCallLlm now explicitly accept an optional Exception, allowing them to automatically set the span status to error and record the exception.
• Refactored Tracing API:
  • traceSendData and other methods now require an explicit Span argument, moving away from implicit context lookups where appropriate.
  • Added traceMergedToolCalls to specifically handle the telemetry for parallel tool executions.
• Flow Logic Cleanup: Simplified Functions.java and BaseLlmFlow.java by removing redundant context passing and aligning with the new consolidated tracing methods.
• Test Suite Updates: Significantly updated ContextPropagationTest.java to reflect the new tracing model. Several manual hierarchy tests were removed in favor of testing the consolidated execute_tool logic and updated attributes.