Copybara import of the project:

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21736067f9 by Alankrit Verma <alankrit386@gmail.com>:

feat(llm_flows): support async before/after tool callbacks

Previously, callbacks were treated as purely synchronous,
so passing an async coroutine caused “was never awaited”
errors and Pydantic serialization failures.

Now we detect awaitable return values from
before_tool_callback and after_tool_callback,
and `await` them if necessary.

Fixes: #380

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08ac9a117e by Alankrit Verma <alankrit386@gmail.com>:

Refactor function callback handling and update type signatures

- Simplify variable names in `functions.py`: always use `function_response` and `altered_function_response`
- Update LlmAgent callback type aliases to support async:
  - Import `Awaitable`
  - Change `BeforeToolCallback` and `AfterToolCallback` signatures to return `Awaitable[Optional[dict]]`
- Ensure `after_tool_callback` uses `await` when necessary

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fcbf57466e by Alankrit Verma <alankrit386@gmail.com>:

refactor: update callback type signatures to support sync and async responses
COPYBARA_INTEGRATE_REVIEW=https://github.com/google/adk-python/pull/434 from AlankritVerma01:support-async-tool-callbacks 926b0ef1a6
PiperOrigin-RevId: 753005846

pyproject.toml

@@ -147,3 +147,4 @@ line_length = 200
 [tool.pytest.ini_options]
 testpaths = ["tests"]
 asyncio_default_fixture_loop_scope = "function"
+asyncio_mode = "auto"