Add basic benchmark

[simonmarty]

Issue #, if available:

Description of changes: Add two basic benchmarks

• One that performs cache hit retrievals
• One that intentionally yields cache misses on every retrieval

Using criterion (used by the AWS SDK for Rust).

This hopefully will serve to catch performance regressions in future code changes and open the door to profiling.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.88%. Comparing base (3613fe4) to head (d4e0aa0).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #122      +/-   ##
==========================================
+ Coverage   91.72%   91.88%   +0.15%     
==========================================
  Files          14       14              
  Lines        2418     2404      -14     
  Branches     2418     2404      -14     
==========================================
- Hits         2218     2209       -9     
+ Misses        150      147       -3     
+ Partials       50       48       -2     

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