Fix hashset perf test

[zhassan-aws]

Description of changes:

The hashset perf test that was added in #2677 currently doesn't run because the perf regressions use the cargo-kani mode, so tests need to be in a cargo package form.

I verified locally that the test is now included:

test [cargo-kani-test] perf/hashset/expected ... ok

Resolved issues:

Related RFC:

Optional #ISSUE-NUMBER.

Call-outs:

Testing:

• How is this change tested? N/A

• Is this a refactor change? No

Checklist

• Each commit message has a non-empty body, explaining why the change was made
• Methods or procedures are documented
• Regression or unit tests are included, or existing tests cover the modified code
• My PR is restricted to a single feature or bugfix

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

[jaisnan]

Thanks!