Benchmark Regression alert

[potsrevennil]

• Resolves #223

• The alert threshold for performance regression is set to 103% for now, let me know if there's any better suggestion for the threshold.

• If the threshold is exceeded, the bench bot will automatically leave a comment on PR like this:

https://github.com/potsrevennil/mlkem-c-aarch64/pull/27

• There will also be GH job summary generated.

• There's some other options provided by the benchmark action (but not set in this pr) which one might be useful as well:

  • fail-on-alert
  • fail-threshold
  • alert-comment-cc-users

[mkannwischer]

Okay, we have to resolve the variance first before proceeding with the alerts. I opened an issue for that: https://github.com/pq-code-package/mlkem-native/issues/429

Turning this into a draft PR for now.

[hanno-becker]

Variance should be fixed now that we have moved c7i to a metal instance. @potsrevennil Can you update this PR?