[FIX] do not apply run found for one task to all tasks

[Remi-Gau]

in dataset with multiple tasks, if a task 'foo' has runs (say from 1 to 10) but another task 'bar' does not, the config was set to look for runs 1 to 10 in all tasks and would return no file for task 'bar' when preparing / generalysing data.

• closes bidsmreye process only one task in the bids_dir #212

[codecov]

Codecov Report

Attention: Patch coverage is 88.88889% with 1 line in your changes missing coverage. Please review.

Project coverage is 82.14%. Comparing base (1bcca23) to head (ca9af5f).
Report is 103 commits behind head on main.

Files with missing lines	Patch %	Lines
bidsmreye/bids_utils.py	75.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #228      +/-   ##
==========================================
+ Coverage   79.91%   82.14%   +2.22%     
==========================================
  Files          13       15       +2     
  Lines         926      952      +26     
  Branches      119        0     -119     
==========================================
+ Hits          740      782      +42     
- Misses        144      170      +26     
+ Partials       42        0      -42     

Flag	Coverage Δ
tests	82.14% <88.88%> (+2.33%)	⬆️

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