draft: Refactor internal data structures of seqvar query schema

[jakibaki]

Solves #374

This keeps the external input of the application unchanged. All that's changed are the internal representations of the data.

[codecov]

Codecov Report

Attention: Patch coverage is 89.09091% with 12 lines in your changes missing coverage. Please review.

Project coverage is 80%. Comparing base (9170afe) to head (ddbd6ac).
Report is 6 commits behind head on main.

Additional details and impacted files

@@         Coverage Diff         @@
##           main   #397   +/-   ##
===================================
  Coverage    80%    80%           
===================================
  Files        43     43           
  Lines      6328   6338   +10     
===================================
+ Hits       5108   5119   +11     
+ Misses     1220   1219    -1     

Files	Coverage Δ
src/seqvars/query/interpreter/frequency.rs	100% <100%> (ø)
src/seqvars/query/interpreter/regions_allowlist.rs	67% <100%> (ø)
src/seqvars/query/mod.rs	88% <100%> (ø)
src/seqvars/query/output/variant_related.rs	79% <100%> (ø)
src/seqvars/query/schema.rs	94% <90%> (-1%)	⬇️
src/seqvars/query/interpreter/clinvar.rs	8% <0%> (ø)

... and 1 file with indirect coverage changes