Pin numpy<2.5 to work around katpoint np.row_stack removal

[sjperkins]

Diagnosis

The scheduled CI run #31663455147 failed on every Python 3.12/3.13/3.14 job (3.11 was green) with a single root cause:

.venv/lib/python3.13/site-packages/xarray_kat/datatree_factory.py:478: in create
    uvw_ant = target.uvw(antennas, scan_timestamps, array_centre)
.venv/lib/python3.13/site-packages/katpoint/target.py:661: in uvw_basis
    u = np.row_stack(np.cross(z, w, axis=0)) * offset_sign
E   AttributeError: module 'numpy' has no attribute 'row_stack'

np.row_stack was deprecated in numpy 2.0 and removed in numpy 2.5.0 (verified: it still exists in 2.4.6). numpy 2.5 requires Python >= 3.12, so the 3.11 jobs resolved to 2.4.x and passed while everything else picked up 2.5.2 (released 2026-08-09, four days before the failing run).

The call site is in katpoint, not in this repo. katpoint fixed it upstream in 122f90d8 ("SPR1-3236 Replace deprecated row_stack with vstack", June 2025), but no release contains it — 0.10.2 (Oct 2024) is still the latest on PyPI.

All 23 failures on 3.12/3.13 and all 14 on 3.14 trace to this one attribute; no other errors were present.

Fix

Add numpy<2.5 to [project].dependencies, with a comment naming the upstream fix so the pin can be dropped once katpoint cuts a release. numpy is imported directly by xarray_kat anyway, so declaring it explicitly is correct regardless.

This is a genuine runtime incompatibility, not just a test-environment issue — UVW computation is core functionality, so any user on numpy >= 2.5 hits it. The constraint therefore belongs in the runtime dependencies rather than the test group.

Verification

Full suite run locally on all four matrix Python versions (resolves to numpy 2.4.6):

Python	Result
3.11	82 passed, 3 skipped
3.12	82 passed, 3 skipped
3.13	82 passed, 3 skipped
3.14	73 passed, 5 skipped

Confirmed the failure reproduces on 3.13 before the change. uv run --dev pre-commit run -a passes.

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