Fix confound generation

[tsalo]

Closes none.

Changes proposed in this pull request

• Confounds (desc-aroma_timeseries.tsv) were being selected by time instead of by component.
• Orthogonalization of confounds was done on zero-padded time series.
• Mixing matrix was written out to derivatives without zero padding.

[codecov]

Codecov Report

Attention: Patch coverage is 7.14286% with 13 lines in your changes missing coverage. Please review.

Project coverage is 30.87%. Comparing base (92bd92b) to head (4dddf70).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/fmripost_aroma/interfaces/confounds.py	0.00%	13 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #67      +/-   ##
==========================================
- Coverage   30.93%   30.87%   -0.07%     
==========================================
  Files          26       26              
  Lines        2324     2329       +5     
  Branches      363      365       +2     
==========================================
  Hits          719      719              
- Misses       1584     1589       +5     
  Partials       21       21              

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