test(all) Add concurrent Lambda invocation tests

[darklight3it]

• chore: add pre commit script for anyone that wants to use it.
• chore: adding new tests

📬 Issue #, if available:

✍️ Description of changes:

This PR adds end-to-end concurrent testing for the basic-lambda-concurrent example using the Lambda Managed Instance (LMI) runtime mode.

What changed

GitHub Actions (.github/workflows/dockerized-test.yml)

• Added dockerized-test-concurrent job that builds only basic-lambda-concurrent, creates a Docker network, and runs the concurrent scenarios via the action

New example behavior (examples/basic-lambda-concurrent/src/main.rs)

• Added a concrete HandlerError type with From<HandlerError> for Diagnostic, giving clean errorType: "HandlerError" in error responses instead of the mangled type name from type_name_of_val
• Added startup log for AWS_LAMBDA_MAX_CONCURRENCY value
• Handler returns Err(HandlerError(...)) for {"command": "fail"} payloads

New test scenarios (test/dockerized/scenarios/concurrent_scenarios.py)

• concurrent_happy_path: fires 10 unique commands concurrently, asserts all succeed
• concurrent_error_isolation: fires 9 failing requests + 1 valid survivor concurrently, asserts the survivor still succeeds despite the errors

Makefile

• Extracted shared Docker setup into build-test-runner target
• Added test-dockerized-concurrent target with Docker network setup for DinD
• TEST_RUNNER_BRANCH variable (defaulting to main, overridable via .env) controls which branch of the test runner is cloned

IMPORTANT

• To make this work I'm running on a custom version of containerized test. We need some more work upstream to make multiconcurrent testing compatible with what we are trying to do.

🔏 By submitting this pull request

• I confirm that I've ran cargo +nightly fmt.
• I confirm that I've ran cargo clippy --fix.
• I confirm that I've made a best effort attempt to update all relevant documentation.
• I confirm that my contribution is made under the terms of the Apache 2.0 license.

[jlizen]

Seems good, I guess the dmelfi/multi-concurrency branch is temporary? Is there a reason it can't go to main?