[WIP] task: validate built-in hmac and fix tests

[Copilot]

Thanks for assigning this issue to me. I'm starting to work on it and will keep this PR's description up to date as I form a plan and make progress.

Original issue description:

The lib/hooks/plugins/auth/hmac.rb file has gotten quite large and unwieldy. Please check it out and ensure it follows ruby best practices, is clean and concise, and fix the failing script/test tests related to it. Do not make any logic breaking changes.

A lot of the logic related to timestamps has gotten quite messy. It passes integration and acceptance tests, but the actual unit test script/test are messy. Please refactor and make this better.

Fixes #31.

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[GrantBirki]

@copilot try again

[GrantBirki]

@copilot try again

[GrantBirki]

@copilot try again

[Copilot]

@copilot try again

I'll restart the approach to fix the failing HMAC tests. Looking at the test failures, there are specific issues with timestamp parsing, validation logic, and regex patterns that need to be addressed.