[PQ] Add experimental support for PQ/T hybrid KEMs

[sgmenda-aws]

Description of changes:

Add an experimental implementation of PQ/T Hybrid KEMs in a new folder crypto/pqt. The header file is crypto/pqt/pqt_kem.h and the source file is crypto/pqt/pqt_kem.c.

These KEMs are plugged into the existing KEM API via crypto/kem/*, and tool/speed.cc is updated to enable benchmarking their performance.

Call-outs:

Lines 399-490 in crypto/pqt/pqt_kem.c contain the core implementation. The rest is boilerplate.

Testing:

These KEMs pass the PerKEMTest suite, minus the test vectors, which will be added in a subsequent commit.

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

Attention: Patch coverage is 92.55814% with 16 lines in your changes missing coverage. Please review.

Project coverage is 78.34%. Comparing base (0574778) to head (08374c5).

Files	Patch %	Lines
crypto/pqt/pqt_kem.c	92.38%	16 Missing ⚠️

Additional details and impacted files

@@                    Coverage Diff                     @@
##           experimental-pq-hybrid    #1741      +/-   ##
==========================================================
+ Coverage                   78.32%   78.34%   +0.01%     
==========================================================
  Files                         580      581       +1     
  Lines                       96618    96833     +215     
  Branches                    13853    13848       -5     
==========================================================
+ Hits                        75679    75862     +183     
- Misses                      20326    20359      +33     
+ Partials                      613      612       -1     

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[torben-hansen]

Still need to review the macrofication.