Minor adjustments to key_wrap module API

[skmcgrail]

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: 5 lines in your changes are missing coverage. Please review.

Comparison is base (cc56479) 95.85% compared to head (7540058) 95.85%.

Files	Patch %	Lines
aws-lc-rs/src/key_wrap.rs	96.71%	5 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #321      +/-   ##
==========================================
- Coverage   95.85%   95.85%   -0.01%     
==========================================
  Files          61       61              
  Lines        8015     8011       -4     
==========================================
- Hits         7683     7679       -4     
  Misses        332      332              

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