KDF in Counter Mode and One-Step KDF API

[skmcgrail]

Description of changes:

Adds support for KDF in Counter Mode and One-Step Key Derivation functions from NIST SP 800-108 and NIST SP 800-56c respectively.

Currently the APIs are under crate::unstable::kdf due to not being able to support this with the fips feature at this time.

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 87.98883% with 43 lines in your changes missing coverage. Please review.

Project coverage is 92.58%. Comparing base (c358484) to head (93d8411).
Report is 54 commits behind head on main.

Files	Patch %	Lines
aws-lc-rs/src/unstable/kdf/sskdf.rs	82.97%	24 Missing ⚠️
aws-lc-rs/src/unstable/kdf/kbkdf.rs	83.82%	11 Missing ⚠️
aws-lc-rs/src/agreement/ephemeral.rs	76.47%	5 Missing and 3 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #482      +/-   ##
==========================================
- Coverage   95.80%   92.58%   -3.22%     
==========================================
  Files          61       66       +5     
  Lines        8143     8812     +669     
  Branches        0     8812    +8812     
==========================================
+ Hits         7801     8159     +358     
- Misses        342      396      +54     
- Partials        0      257     +257     

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[samuel40791765]

Very minor nit, is there a better way to iterate over these with something like a macro?

[justsmth]

Yeah, it is possible to have a variadic macro, but given the subtle differences between each of the macro invocations below, a variadic mecro for this would likely be much less pleasant.