feat: shutdown messages

[WinPlay02]

Closes #24

Summary of Changes

• added a shutdown message type that can be sent by the extension to gracefully shut down the runner
• the sync child process should be shut down when sending a shutdown message

[codecov[bot]]

Codecov Report

Attention: 11 lines in your changes are missing coverage. Please review.

Comparison is base (fc5934f) 100.00% compared to head (d32f769) 81.37%.

Files	Patch %	Lines
tests/safeds_runner/server/test_websocket_mock.py	15.38%	11 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #25 +/- ## ============================================ - Coverage 100.00% 81.37% -18.63% ============================================ Files 9 10 +1 Lines 337 435 +98 ============================================ + Hits 337 354 +17 - Misses 0 81 +81 ```

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[github-actions[bot]]

🦙 MegaLinter status: ✅ SUCCESS

Descriptor	Linter	Files	Fixed	Errors	Elapsed time
✅ PYTHON	black	4	0	0	0.61s
✅ PYTHON	mypy	4		0	1.72s
✅ PYTHON	ruff	4	0	0	0.03s
✅ REPOSITORY	git_diff	yes		no	0.02s

See detailed report in MegaLinter reports _Set VALIDATE_ALL_CODEBASE: true in mega-linter.yml to validate all sources, not only the diff_

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[WinPlay02]

Why is the coverage suddenly broken?

[lars-reimann]

Why is the coverage suddenly broken?

No idea. For some reason, the test file is included in the coverage after 11108bb.

[lars-reimann]

:tada: This PR is included in version 0.4.0 :tada:

The release is available on:

• v0.4.0
• GitHub release

Your semantic-release bot :package::rocket: