Feature: Runtime Execution Simulator

Name Pending.

Testing Lambda code can be difficult / unwieldy. While SAM exists for all supported languages, it is pretty limited in ergonomics, difficult to integrate with in CI, makes testing / infrastructure management unnecessarily complicated, and still requires further orchestration.

In an ideal world, we'd be able to "just" create a runtime with the corresponding service, add all the hooks, tracking, and tracing that we need, execute requests on top, and then verify the results, benchmark, get flamegraphs, etc, all without actually ever deploying, and all from a single `tokio::test`.

I have added a basic server in #1086, so this backlog issue is for extension / reuse of the implementation.

We should start from an internal implementation, and eventually publish a crate so that users can depend on it and integrate it in their CI.

Use the basic server added in issue #1086 as the entry point, then review how it could be extended or reused for local runtime execution. Before implementing, clarify the first internal milestone and acceptance criteria, since the issue currently spans hooks, tracing, request execution, benchmarking, and eventual crate publication.

Written by the indexing model from the issue text.