feat: Exclude non-steady-state volumes from confoundplot bounds, stats

[effigies]

Includes nipreps/nireports#206.

Basically a smoke test to make sure that it works. ds005 and ds210 both have non-zero non-steady-state volumes.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 73.61%. Comparing base (c961b3c) to head (c983d7f).
⚠️ Report is 78 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3499      +/-   ##
==========================================
+ Coverage   73.50%   73.61%   +0.11%     
==========================================
  Files          60       60              
  Lines        4582     4609      +27     
  Branches      585      586       +1     
==========================================
+ Hits         3368     3393      +25     
- Misses       1085     1087       +2     
  Partials      129      129              

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[effigies]

This will be included in the release when we set the nireports pin.