refactor ptls to clarify the difference between FIPS and non-FIPS modes

[cfryanr]

and backfill some basic tests

Release note:

NONE

[codecov]

Codecov Report

Attention: Patch coverage is 95.60440% with 4 lines in your changes are missing coverage. Please review.

Project coverage is 29.40%. Comparing base (f96cbea) to head (e13f4a7).

Files	Patch %	Lines
internal/crypto/ptls/profiles.go	96.66%	3 Missing ⚠️
internal/crypto/ptls/ptls.go	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1950      +/-   ##
==========================================
+ Coverage   29.39%   29.40%   +0.01%     
==========================================
  Files         349      348       -1     
  Lines       58484    58499      +15     
==========================================
+ Hits        17190    17201      +11     
- Misses      40780    40783       +3     
- Partials      514      515       +1     

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