[CHORE]: Support Python 3.13 (requires numpy 2.x migration) #303

Title: Support Python 3.13 (requires numpy 2.x migration)

Body:

Currently blocked on numpy<2. numpy 1.x has no cp313 wheels on PyPI, which
caused broken installs on Python 3.13 (fixed in v0.2.1 by lowering the
supported Python ceiling to <3.13).

Plan

1. Loosen numpy<2 → numpy<3 in pyproject.toml
2. Fix any numpy 2.x API breaks in the codebase:
   • np.float_ → np.float64
   • np.NaN → np.nan
   • np.in1d → np.isin
   • np.trapz → np.trapezoid
   • np.product / np.cumproduct → np.prod / np.cumprod
3. Verify transitive deps at numpy 2:
   • numba >= 0.60
   • librosa >= 0.10.2
   • scipy >= 1.13
   • torch >= 2.3
4. Run full verify_release.sh on 3.13 with real audio
5. Add 3.13 to tests.yml matrix
6. Restore requires-python = "<3.14" in pyproject.toml

Target

v0.2.1+

Related

• v0.2.1 patch