improv(idempotency): consolidate internal implementation - #1642

Description of your changes

This PR introduces a refactor of the IdempotencyHandler and makeHandlerIdempotent Middy middleware so that the latter uses logic from the former rather than duplicating logic.

Prior to this PR the middleware was reimplementing some of the logic found in the IdempotencyHandler because at the time of implementing the handler its logic was not taking into account the request lifecycle that Middy middlewares use to handle requests.

The PR adds some new methods/hooks to the handler so that most of the idempotency logic still resides in the handler. Some of the actions still need to be manual due to how Middy works, a different approach would require a complete refactor of the IdempotencyHandler class.

Related issues, RFCs

Issue number: #1508

Checklist

• My changes meet the tenets criteria
• I have performed a self-review of my own code
• I have commented my code where necessary, particularly in areas that should be flagged with a TODO, or hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my change is effective and works
• The PR title follows the conventional commit semantics

Breaking change checklist

Is it a breaking change?: NO

• I have documented the migration process
• I have added, implemented necessary warnings (if it can live side by side)

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