Adds AES CBC mode no padding

[Elvrarin]

Issues:

See SIM P307101963

Description of changes:

Currently, only the PaddedBlock keys and Streaming keys supports CBC mode.
This adds CBC mode for EncryptingKey and DecryptingKey. This allows AES CBC encryption/decryption with no padding.

Call-outs:

Since no padding is used, input data must be block aligned, length of input must be a multiple of 16 bytes.
I also included the DANGER message in the doc string, since I think the use of this is unconventional.

Testing:

Unit tests added following examples of existing unit tests.

KAT

Added known-answer tests from "Appendix F" of SP800-38a:

• https://nvlpubs.nist.gov/nistpubs/Legacy/SP/nistspecialpublication800-38a.pdf

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.
✅ Project coverage is 92.36%. Comparing base (c358484) to head (6bcc4a8).
⚠️ Report is 263 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #895      +/-   ##
==========================================
- Coverage   95.80%   92.36%   -3.44%     
==========================================
  Files          61       73      +12     
  Lines        8143     9659    +1516     
  Branches        0     9659    +9659     
==========================================
+ Hits         7801     8922    +1121     
- Misses        342      450     +108     
- Partials        0      287     +287     

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[Elvrarin]

the same code would succeed for some inputs and fail for others at runtime.

I agree this is a bit confusing, but the existing ECB mode for EncryptKey and DecryptKey also behaves the same way, that is to require input size to be block-aligned. There is the "skull emoji" DANGER message that will be shown on the docs.rs, I think it already push consumers off of these API, save for those who understands the intricacies of ECB mode.

The larger API/feature flag refactoring is beyond what I can single handedly do. Let me know how I can help here. Thanks.