maint: remove numba as a direct dependency (#483)

[SaguaroDev]

Closes #483.

numba is listed in [project.dependencies] (numba>0.54) but is not imported anywhere in the package — a grep of the chainladder/ tree returns no import numba / from numba.

As @jbogaardt noted on the issue, numba is a hard dependency of sparse, which chainladder depends on directly. I confirmed this against the current pin: sparse 0.17.0 declares numba>=0.49, so numba is still installed transitively after removing the direct entry. @genedan's 2026-05-18 comment proposed exactly this for 0.9.3.

Removing the direct pin also stops chainladder from constraining numba independently of sparse, which is what was causing the numpy-compatibility friction reported earlier in the thread (the chainladder-pinned numba lagging numpy).

Verification

• With numba>0.54 removed from [project.dependencies], uv pip install -e ".[dev]" re-resolves the environment and numba is still present: numba 0.63.1 (pulled via sparse).
• Full suite: 717 passed, 12 xfailed (the xfails and warnings are pre-existing, unchanged from a clean run).

Single-line change to pyproject.toml. Happy to adjust if you'd prefer to also set a numba floor somewhere explicit, but since it's transitive-only now I left it to sparse to constrain.

---

Note

Low Risk
Single-line dependency metadata change; numba remains via sparse and the suite was verified unchanged.

Overview
Removes numba>0.54 from pyproject.toml [project.dependencies]. The package does not import numba directly; it remains available transitively via sparse, so install graphs still include numba without chainladder imposing its own pin.

That avoids an extra, package-level numba constraint that could drift from sparse’s requirements and contribute to numpy/numba compatibility friction.

^{Reviewed by Cursor Bugbot for commit 899d808. Bugbot is set up for automated code reviews on this repo. Configure here.}

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.90%. Comparing base (8a9a46e) to head (899d808).

Additional details and impacted files

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##             main     #898   +/-   ##
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  Coverage   86.90%   86.90%           
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  Files          87       87           
  Lines        4932     4932           
  Branches      624      624           
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  Hits         4286     4286           
  Misses        456      456           
  Partials      190      190           

Flag	Coverage Δ
unittests	86.90% <ø> (ø)

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