Fix annotate_muscle_zscore crash with n_jobs='cuda'

[kveni12]

Fixes #13993

Summary

• Add n_jobs_hilbert parameter to annotate_muscle_zscore so filtering and Hilbert transform can use separate parallelization settings
• Filtering continues to accept n_jobs='cuda' while Hilbert defaults to n_jobs=1 when n_jobs_hilbert is not set
• Add tests covering n_jobs='cuda', explicit integer n_jobs/n_jobs_hilbert, and unchanged default behavior

Test plan

• Smoke-tested locally with synthetic data (n_jobs='cuda', n_jobs=4/n_jobs_hilbert=2, default)
• CI: mne/preprocessing/tests/test_artifact_detection.py::test_muscle_annotation_n_jobs_cuda
• CI: existing test_muscle_annotation tests

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[larsoner]

Hmmm... this isn't backward compatible. Previously, if a user provided n_jobs=4 for example, this would use 4 jobs. So a better pattern I think is:

if n_jobs != "cuda" and n_jobs_hilbert is None:
    n_jobs_hilbert = n_jobs

And you say in the docstring that n_jobs_hilbert will default to the value of n_jobs when n_jobs != "cuda".