Annotate every function in the package and its tests

[roytsmart]

Adds type annotations to every function in the package and its tests that was missing them. There are no behavior changes.

Package (13 functions)

• Clipping kernel bodies: area_signed, num_pair and clip_cell, which build() compiles for each target. They now match the module-level helpers beside them, which were already annotated.
• CUDA kernels: _fill, _scatter, count_cells and clip_cells. Device arrays are annotated as Any, as they already are where the host passes them in, because numba ships no type for DeviceNDArray.
• Host: _jit() in the clipping kernel.
• Return types and **kwargs: sign() -> int, index_in_bounds() -> bool, ndarray_linear_interpolation() -> np.ndarray, _calc_and_save_weights() -> None, and fill(**kwargs: Any).

Numba ignores annotations, so the compiled kernels are unchanged.

Tests (154 functions)

• -> None: added to every test function (133, done mechanically).
• Helpers: the helpers and nested helpers (_grids, _lattice, _flat, _triple, dense, totals, ...) are annotated by hand.
• Parametrized tests: the untyped parameters of four parametrized tests are typed (dtype, func, unit).

Checks

• An AST scan finds no function in regridding/ without full annotations.
• Pyright at CI's 1.1.411 with the repo config is unchanged.
• The tests are excluded from pyright in pyproject.toml, and pyright skips an excluded file even when it is named on the command line. I therefore checked them with a temporary config that includes them:
  • On main: 127 errors.
  • With this PR: 81 errors, none of them new. The annotations remove 46.
  • What remains: errors that already existed, mostly astropy unit expressions and keyword arguments collected with dict(...) and splatted.
• Full suite locally, including the CUDA tests on an RTX 4090: 405 passed and 2 xfailed. black and ruff pass.
• A real trial merge with Add convolve_weights() to fold a point-spread function into a set of weights #67 is clean, and the merged tree is fully annotated with its tests passing.

🤖 Generated with Claude Code

https://claude.ai/code/session_01GqceVSp8s2msxj1Dr9MrGU

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.62%. Comparing base (a3966eb) to head (f7d7cd8).

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #68   +/-   ##
=======================================
  Coverage   99.62%   99.62%           
=======================================
  Files          55       55           
  Lines        3188     3192    +4     
=======================================
+ Hits         3176     3180    +4     
  Misses         12       12           

Flag	Coverage Δ
unittests	99.62% <100.00%> (+<0.01%)	⬆️

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

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.