Fix error with sub- prefixes in FilterResultdicts

[HippocampusGirl]

Also add regression test

[codecov]

Codecov Report

Merging #264 (cb50afc) into main (8870286) will increase coverage by 0.61%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #264      +/-   ##
==========================================
+ Coverage   62.19%   62.81%   +0.61%     
==========================================
  Files         218      218              
  Lines       12063    12071       +8     
  Branches     2408     2408              
==========================================
+ Hits         7503     7582      +79     
+ Misses       4114     4029      -85     
- Partials      446      460      +14     

Impacted Files	Coverage Δ
halfpipe/interface/resultdict/filter.py	64.57% <100.00%> (+44.21%)	⬆️

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