Bugfix: ZapLine sampling rate mismatch & Changelog setup

[BabaSanfour]

• Added Towncrier changelog system and configuration
• Updated CONTRIBUTING.md with new guidelines
• Fixed ZapLine sampling rate mismatch bug (Fixes Fix ZapLine failure when sampling rate is not a multiple of line frequency #16)
• Added adaptive ZapLine tests

[codecov]

Codecov Report

❌ Patch coverage is 94.11765% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 90.34%. Comparing base (db23c8f) to head (a2fed1d).
⚠️ Report is 7 commits behind head on main.

Files with missing lines	Patch %	Lines
mne_denoise/zapline/adaptive.py	86.66%	0 Missing and 2 partials ⚠️
mne_denoise/zapline/core.py	96.00%	0 Missing and 2 partials ⚠️
mne_denoise/dss/denoisers/spectral.py	91.66%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #17      +/-   ##
==========================================
+ Coverage   89.71%   90.34%   +0.62%     
==========================================
  Files          32       32              
  Lines        2547     2588      +41     
  Branches      447      454       +7     
==========================================
+ Hits         2285     2338      +53     
+ Misses        153      144       -9     
+ Partials      109      106       -3     

Flag	Coverage Δ
unittests	90.34% <94.11%> (+0.62%)	⬆️

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Files with missing lines	Coverage Δ
mne_denoise/dss/denoisers/temporal.py	100.00% <100.00%> (ø)
mne_denoise/dss/linear.py	96.72% <ø> (ø)
mne_denoise/dss/denoisers/spectral.py	99.00% <91.66%> (+9.62%)	⬆️
mne_denoise/zapline/adaptive.py	93.42% <86.66%> (+0.17%)	⬆️
mne_denoise/zapline/core.py	97.93% <96.00%> (+0.91%)	⬆️

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[BabaSanfour]

Doc is failing due to an issue in mne-python related to tarfile security filters in Python 3.12+ (mne-tools/mne-python#13648). Will merge and close and bump mne version once fix is released.