Expect flat bids_filters across package

[tsalo]

Closes #109. We might need to overwrite these changes when we address #101. It might also make it harder to fix #108. Actually I think I can fix #108 by using the bids_filters directly.

Changes proposed in this pull request

• Reduce any cases that expect bids_filters to be a nested dictionary (e.g., {"bold": {"acquisition": "good"}}) to instead expect a flat dictionary that only applies to the BOLD data (e.g., {"acquisition": "good"}).

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 2 lines in your changes missing coverage. Please review.

Project coverage is 30.84%. Comparing base (c3390c3) to head (a71b628).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/fmripost_aroma/config.py	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #110      +/-   ##
==========================================
+ Coverage   30.83%   30.84%   +0.01%     
==========================================
  Files          26       26              
  Lines        2374     2373       -1     
  Branches      289      288       -1     
==========================================
  Hits          732      732              
+ Misses       1619     1618       -1     
  Partials       23       23              

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