Improve performance of vcf-variant->protein-hgvs

[totakke]

Improves performance of vcf-variant->protein-hgvs by optimizing amino acid conversion and sequence retrieving. That can be checked with libra benchmark code.

before (commit 3ec5ed6):

$ lein libra :only varity.vcf-to-hgvs-bench

Measuring varity.vcf-to-hgvs-bench

vcf-variant->protein-hgvs-bench (vcf_to_hgvs_bench.clj:19)

  time: 97.077914 ms, sd: 113.403155 µs

after (commit ac184f7):

$ lein libra :only varity.vcf-to-hgvs-bench

Measuring varity.vcf-to-hgvs-bench

vcf-variant->protein-hgvs-bench (vcf_to_hgvs_bench.clj:19)

  time: 26.393281 ms, sd: 597.575155 ns

I confirmed lein test :all passed.

[codecov]

Codecov Report

Merging #22 into master will increase coverage by 0.14%.
The diff coverage is 37.5%.

@@            Coverage Diff            @@
##           master     #22      +/-   ##
=========================================
+ Coverage   38.96%   39.1%   +0.14%     
=========================================
  Files          13      13              
  Lines        1468    1460       -8     
  Branches       31      31              
=========================================
- Hits          572     571       -1     
+ Misses        865     858       -7     
  Partials       31      31

Impacted Files	Coverage Δ
src/varity/vcf_to_hgvs/protein.clj	29.19% <0%> (+0.62%)	⬆️
src/varity/codon.clj	100% <100%> (ø)	⬆️

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[federkasten]

Thanks. LGTM 🙆‍♂️
I have also confirmed these changes improve the performance drastically.