Refactor pgp_fingerprint_t and pgp_keyid_t.

[ni4]

Fixes #2110

[codecov]

Codecov Report

Attention: Patch coverage is 92.80000% with 9 lines in your changes missing coverage. Please review.

Project coverage is 85.27%. Comparing base (6a01b03) to head (56d39c1).
Report is 10 commits behind head on main.

Files with missing lines	Patch %	Lines
src/lib/fingerprint.cpp	89.65%	3 Missing ⚠️
src/librepgp/stream-dump.cpp	82.35%	3 Missing ⚠️
src/lib/key.cpp	92.00%	2 Missing ⚠️
src/librekey/key_store_pgp.cpp	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2331      +/-   ##
==========================================
+ Coverage   85.23%   85.27%   +0.03%     
==========================================
  Files         124      125       +1     
  Lines       22858    22813      -45     
==========================================
- Hits        19484    19453      -31     
+ Misses       3374     3360      -14     

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[maxirmx]

LGTM

[ni4]

Merging with two approvals. Thanks!