feat: Improving LoggingPlugin

[copybara-service]

feat: Improving LoggingPlugin

This CL refactors and improves the LoggingPlugin in the ADK core.

Here's a summary of the changes:

1. Consistent Agent Name Logging: The plugin now consistently retrieves the agent name from callbackContext.agentName() in beforeAgentCallback and afterAgentCallback, instead of using agent.name().

2. Enhanced LLM Response Logging: The formatContent method has been significantly updated to provide more detailed logging for different types of Content.parts() within an LLM response. It now explicitly logs:

   • Trimmed and potentially truncated text.
   • The name of functionCall and functionResponse.
   • Indicators for codeExecutionResult and other part types.
     The different parts are joined by " | ".

3. Improved Optional Field Logging: Optional fields like llmResponse.errorMessage() and toolContext.functionCallId() are now always logged, displaying "None" when the optional is empty, rather than only logging when the value is present.

4. Simplified Argument Formatting: The formatArgs method now uses args.toString() for formatting, simplifying the code while still handling truncation for long argument strings.

5. Removed Redundant Error Logging: Duplicate logger.error calls within onLlmError and onToolError have been removed, as the preceding log calls already capture the necessary error information.

6. Test Updates: LoggingPluginTest.java has been updated to mock mockCallbackContext.invocationContext() and remove an unnecessary mock for mockCallbackContext.branch().