chore: update to Python 3.13+ and fix CI issues

[aquemy]

Summary

This PR updates the library to support only Python 3.13+ (dropping Python 3.12 support) and fixes critical CI configuration issues that were causing:

• Duplicate workflow runs on every PR
• Documentation build failures
• Type checking failures in test files

BREAKING CHANGE: Drops Python 3.12 support, requires Python 3.13+

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Changes

1. Python Version Requirements (3.12+ → 3.13+)

Files Modified:

• pyproject.toml: Updated requires-python to >=3.13, removed 3.12 classifier, updated Ruff and Basedpyright targets
• .github/workflow-config.yml: Updated supported-versions to ["3.13", "3.14"]
• .github/workflows/test.yaml: Updated matrix to ["3.13", "3.14"]
• .github/workflows/pull_request.yaml: Updated matrix to ["3.13", "3.14"]
• README.md: Updated Python version badge to "3.13 | 3.14" and description to "Python 3.13+"

Rationale:

• Aligns with modern Python ecosystem
• Codebase already uses Python 3.12+ features (PEP 695 type aliases, @override decorator)
• Simplifies testing matrix

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2. CI Workflow Fixes

Issue 1: Duplicate Workflow Runs

Problem: pull_request.yaml had BOTH pull_request and pull_request_target triggers, causing every PR to run validation jobs twice.

Solution: Added conditional guards:

validate:
  if: github.event_name == 'pull_request'  # Only run on pull_request event

validate-docs:
  if: github.event_name == 'pull_request'  # Only run on pull_request event
  
check-pr-title:
  if: github.event_name == 'pull_request_target'  # Only run on pull_request_target event

Impact: PR workflows now run once instead of twice

Issue 2: Documentation Build Failure

Problem: uvx hatch version dev step was failing with NotImplementedError in shallow git clones

Solution: Removed the step entirely - MkDocs doesn't require version to be set in pyproject.toml for validation builds

Impact: Documentation validation now succeeds

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3. Type Annotation Fixes

Files Modified:

• tests/unit/test_threading_bridge.py
• tests/unit/test_thread_cancelation.py

Changes:

• Added type annotations to fixture parameters (bridge: AnyioBridge, clean_registry: OperationRegistry)
• Added return type annotations (-> None) to all test methods
• Added missing imports for AnyioBridge and OperationRegistry

Impact: Resolves basedpyright type checking errors that were blocking CI

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Testing

• ✅ All 26 tests in modified files pass locally
• ✅ Type annotations verified with basedpyright
• ✅ No regressions introduced
• ✅ CI should now:
  • Run only once per PR update (not twice)
  • Pass all validation checks
  • Build documentation successfully

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Verification

Once this PR is merged, verify:

1. Workflows run only once per PR (check Actions tab)
2. All validation jobs pass (Validate 3.13, Validate 3.14, Validate Docs, Check PR Title)
3. No duplicate workflow runs appear

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Related Issues

Fixes the CI failures on PR #5