CMAC: sign_to_buffer and Context::verify

[justsmth]

Description of changes:

Adds functions cmac::sign_to_buffer and cmac::Context::verify:

• cmac::sign_to_buffer allows the caller to provide their own buffer into which the tag will be written.
• cmac::Context::verify allows for verification of multi-part data.

Testing:

Updated/expanded testing around cmac.

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

❌ Patch coverage is 94.44444% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 92.62%. Comparing base (c358484) to head (5706fee).
⚠️ Report is 297 commits behind head on main.

Files with missing lines	Patch %	Lines
aws-lc-rs/src/cmac.rs	94.44%	2 Missing and 4 partials ⚠️

Additional details and impacted files

@@ Coverage Diff @@ ## main #968 +/- ## ========================================== - Coverage 95.80% 92.62% -3.18%  ========================================== Files 61 74 +13 Lines 8143 9982 +1839 Branches 0 9982 +9982 ========================================== + Hits 7801 9246 +1445  - Misses 342 452 +110  - Partials 0 284 +284 

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