feat: allow returning None for query interfaces (#255)

[holtgrewe]

No description provided.

[codecov]

Codecov Report

Attention: 41 lines in your changes are missing coverage. Please review.

Comparison is base (dd4eecc) 71.07% compared to head (d9f8938) 70.95%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #256      +/-   ##
==========================================
- Coverage   71.07%   70.95%   -0.12%     
==========================================
  Files          60       60              
  Lines        5680     5729      +49     
==========================================
+ Hits         4037     4065      +28     
- Misses       1643     1664      +21     

Files	Coverage Δ
src/clinvar_minimal/cli/query.rs	93.91% <77.77%> (+0.16%)	⬆️
src/dbsnp/cli/query.rs	93.20% <77.77%> (+0.17%)	⬆️
src/tsv/cli/query.rs	91.86% <80.00%> (-0.45%)	⬇️
src/freqs/cli/query.rs	91.81% <89.28%> (-2.13%)	⬇️
src/gnomad_mtdna/cli/query.rs	93.24% <66.66%> (-0.51%)	⬇️
src/gnomad_nuclear/cli/query.rs	93.91% <66.66%> (-0.53%)	⬇️
src/helixmtdb/cli/query.rs	93.24% <66.66%> (-0.51%)	⬇️
src/genes/cli/query.rs	0.00% <0.00%> (ø)
src/clinvar_genes/cli/query.rs	0.00% <0.00%> (ø)

... and 1 file with indirect coverage changes

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