fix(autogen-ext): clean up temporary output dir in JupyterCodeExecutor

[weiguangli-io]

Summary
This PR fixes a resource leak in JupyterCodeExecutor when output_dir is not provided.

Closes #7217.

Problem
JupyterCodeExecutor creates a temporary output directory by default, but stop() did not clean it up. In long-running/local-dev workflows this leaves temp directories behind.

Changes

• Track ownership of the output directory (_owns_output_dir).
• Use TemporaryDirectory for default output directory lifecycle management.
• Clean up owned temp output directory in stop().
• Re-create an owned temp output directory in start() after a previous stop() to keep restart() behavior safe.
• Add regression tests for:
  • default temp output dir cleanup on stop
  • custom output dir preservation on stop
  • fallback behavior for unknown mime/output types
  • restart path recreating default temp output dir

Validation
Local checks run and passed:

• uv run ruff check python/packages/autogen-ext/src/autogen_ext/code_executors/jupyter/_jupyter_code_executor.py python/packages/autogen-ext/tests/code_executors/test_jupyter_code_executor.py
• cd python && uv run mypy packages/autogen-ext/src/autogen_ext/code_executors/jupyter/_jupyter_code_executor.py packages/autogen-ext/tests/code_executors/test_jupyter_code_executor.py
• cd python && uv run pytest packages/autogen-ext/tests/code_executors/test_jupyter_code_executor.py -q
• cd python && uv run pytest packages/autogen-ext/tests/code_executors/test_jupyter_code_executor.py -q --cov=autogen_ext.code_executors.jupyter._jupyter_code_executor --cov-report=term-missing

Coverage for autogen_ext.code_executors.jupyter._jupyter_code_executor in this test run: 100%.

[weiguangli-io]

Closing — the autogen repo has shifted to maintenance mode and external PRs are no longer being reviewed. Thank you for the great framework!