Fix 7 Google ADK examples that crash with SpawnSafetyError

[kowser-orkes]

Pull Request type

• Bugfix
• Feature
• Refactoring (no functional changes, no api changes)
• Build related changes
• WHOSUSING.md
• Other (please describe):

NOTE: Please remember to run poetry run ruff format && poetry run ruff check --fix to fix
any format violations.

Changes in this PR

• examples/agents/adk/14_callbacks.py-20_blog_writer.py (7 files) defined tool functions as
  closures nested inside main() — raises SpawnSafetyError at registration, since spawn
  can't pickle a function with qualname main.<locals>.fn.
• Fix: hoisted the tool defs to module level, matching every other example. No behavior change.
• Standard Python multiprocessing limitation, not an SDK or ADK bug — docs/WORKER.md states
  the same rule for @worker_task workers.

Issue #443

Alternatives considered

• SDK-side workaround (cloudpickle, or fork instead of spawn) — rejected, fork is unsafe
  on macOS (native-framework SIGSEGV), which is why spawn is the default.
• Leave examples non-runnable, document instead of fix — rejected, every other example runs.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
see 60 files with indirect coverage changes

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