fix: restore contexts after exceptions

[xelandernt]

Summary

Restore State and async ContextResource cleanup after exceptional exits.

Changes

• Reset state context tokens in finally.
• Tear down async resources and restore their tokens in finally.
• Added nested and exceptional-context regressions.

Checklist

• Lint and format pass (ruff)
• Type check passes (mypy and pyrefly)
• Tests pass and new behavior is covered
• Build succeeds (uv build) if packaging or build config changed
• Docs updated if behavior or public API changed
• Repo metadata stays consistent across the three surfaces (GitHub description, pyproject description, profile blurb) if this touches packaging

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

Flag	Coverage Δ
unittests	100.00% <100.00%> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
tests/providers/test_context_resources.py	100.00% <100.00%> (ø)
tests/providers/test_state.py	100.00% <100.00%> (ø)
that_depends/providers/context_resources.py	100.00% <100.00%> (ø)
that_depends/providers/state.py	100.00% <100.00%> (ø)

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[xelandernt]

@lesnik512 Can you please remove the Type check passes (ty) from the PR checklist? It is not relevant for this repo.

[lesnik512]

#234