RSA KeyPair improvements, TlsProtocolId fix, and API documentation improvements

[skmcgrail]

Description of changes:

• Improve API reference documentation
• Mark TlsProtocolId as non_exhaustive
• Reduce multiple RSA key verification calls

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license and the ISC license.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (1bdaefe) 95.61% compared to head (4dc1abd) 95.46%.
Report is 3 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #268      +/-   ##
==========================================
- Coverage   95.61%   95.46%   -0.15%     
==========================================
  Files          50       50              
  Lines        6699     6701       +2     
==========================================
- Hits         6405     6397       -8     
- Misses        294      304      +10     

Files	Coverage Δ
aws-lc-rs/src/aead/tls.rs	82.94% <ø> (ø)
aws-lc-rs/src/lib.rs	97.22% <ø> (ø)
aws-lc-rs/src/rsa.rs	93.53% <ø> (+0.10%)	⬆️

... and 1 file with indirect coverage changes

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