[MAINT] ASR: fit_eeg_distribution docstring fixes + asr_calibrate input guards

[sappelhoff]

A small bundle of documentation and defensive-hardening fixes:

• fit_eeg_distribution docstring: the min_clean_fraction / max_dropout_fraction default values were transposed relative to the signature (0.25 / 0.1); corrected. Also X was described as a 2-D (n_channels, n_samples) array, but the function operates on a 1-D vector of amplitude values (it does np.sort(X); n=len(X)) — description fixed.
• asr_calibrate non-finite guard: a NaN/Inf in the calibration data previously propagated silently through the filter into M/T (an all-NaN threshold, no error). Non-finite samples are now zeroed before filtering so calibration degrades gracefully.
• asr_calibrate insufficient-data guards: raise a clear ValueError when the calibration data is too short to form one analysis window, or yields fewer than two threshold-estimation windows — instead of an obscure downstream error.

Testing

Adds tests that non-finite calibration input yields finite M/T, and that too-short calibration raises a clear ValueError. Full tests/test_asr.py + tests/test_cov.py pass; ruff clean.

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Note: includes the nonlinear_eigenspace reproducibility fix from #118 so the riemann CI test is stable regardless of what this PR changes. Once #118 merges first, that commit drops out on rebase.

[codecov]

Codecov Report

❌ Patch coverage is 80.00000% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 83.10%. Comparing base (d2f4494) to head (5e14dd6).

Files with missing lines	Patch %	Lines
meegkit/asr.py	80.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #121      +/-   ##
==========================================
- Coverage   83.10%   83.10%   -0.01%     
==========================================
  Files          25       25              
  Lines        2818     2823       +5     
==========================================
+ Hits         2342     2346       +4     
- Misses        476      477       +1     

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