key_pair: add function to retrieve signature algorithm

[tindzk]

Purpose

Currently, the alg field is restricted to the crate's scope.

Changes

Provide a public function to access signature algorithm.

Checklist

• Self-review has been completed
• Changes are complete and ready for review
• Changes are covered by existing or new tests

[codecov]

Codecov Report

Merging #158 (095633c) into main (31403a4) will increase coverage by 0.33%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #158      +/-   ##
==========================================
+ Coverage   71.90%   72.24%   +0.33%     
==========================================
  Files           7        7              
  Lines        1876     1888      +12     
==========================================
+ Hits         1349     1364      +15     
+ Misses        527      524       -3     

Files Changed	Coverage Δ
src/key_pair.rs	72.27% <100.00%> (+3.04%)	⬆️

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[cpu]

This seems reasonable to me, thanks!

[cpu]

ci / Documentation (nightly) (pull_request) Failing after 26s

Going to administratively merge this. The num-traits crate fixed the custom_code_classes_in_docs error w/ nightly but it isn't in a released version yet.