X5CVerifier: support for RSA

[m-barthelemy]

After #238 adding support for .es256, .es384, .es512 and .eddsa, this PR adds support for RSA signatures.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 82.85%. Comparing base (a93a262) to head (7e985b2).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #244      +/-   ##
==========================================
+ Coverage   82.20%   82.85%   +0.65%     
==========================================
  Files          61       61              
  Lines        1472     1505      +33     
==========================================
+ Hits         1210     1247      +37     
+ Misses        262      258       -4     

Files with missing lines	Coverage Δ
Sources/JWTKit/X5C/X5CVerifier.swift	89.25% <100.00%> (+4.02%)	⬆️

... and 1 file with indirect coverage changes

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