Migrate tests/test_gpu_stump.py to npt.assert_allclose

[viknesh-ai]

Related to #1175

tests/test_gpu_stump.py (36 sites) — same shape as test_gpu_aamp.py. Renamed comp_mp to cmp_mp, flipped order, cast to float64 since naive.stump() mixes distance/index columns (dtype=object), same root cause as the earlier files. A few sites keep the config.STUMPY_TEST_PRECISION reference instead of the 1.5e-07 literal. Commented-out pd.Series variants updated too, left commented.

Only runs under CUDA, verified locally with NUMBA_ENABLE_CUDASIM=1: 39/39 passing.

To Do List

• assert_allclose, cmp first
• atol=1.5e-07 / config reference where it was
• cmp not comp
• ref_/cmp_ naming, cast where needed

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[gitnotebooks]

Review these changes at https://app.gitnotebooks.com/stumpy-dev/stumpy/pull/1197

[viknesh-ai]

@seanlaw next one — same conventions as before.