Unblock editable installs on Python 3.12+ and update run-tests workflow for current GitHub runners

[Copilot]

pip -e . failed on newer Python because setup.py imported NumPy at build time, which breaks under build isolation. After fixing packaging, CI still failed because the workflow used deprecated Actions and Python versions unavailable on current hosted runners.

• Packaging: remove build-time NumPy coupling

  • Dropped import numpy from setup.py.
  • Removed setup-time fields that required NumPy during build (include_dirs, setup_requires).
  • Kept NumPy in install_requires, so runtime dependency behavior remains unchanged.

• CI workflow: align with supported runner/toolchain versions

  • Upgraded workflow actions:
    • actions/checkout@v2 → @v4
    • actions/setup-python@v1 → @v5
  • Updated Python matrix to versions available on current runners:
    • Ubuntu: 3.10, 3.11, 3.12
    • macOS/Windows: 3.10
  • Set shell: bash for script-based steps to run ./run-tests.sh consistently across OS jobs.

strategy:
  matrix:
    python-version: ["3.10", "3.11", "3.12"]

- uses: actions/setup-python@v5
  with:
    python-version: ${{ matrix.python-version }}