Issue #3615511: Add runtime requirements and uninstall hooks to myrest.install

Adds myrest_runtime_requirements() - the 11.3 replacement for the deprecated phase-based hook_requirements() - warning about missing credentials and the MD5 hashing algorithm, erroring while secrets are still in configuration, and summarising the API configuration when nothing is wrong.

myrest_uninstall() deletes the three state keys. It deliberately leaves configuration alone: core removes what a module ships in config/install, while state has no owner and would keep the credentials of an uninstalled module.

The issue's premise about REPLACE_WITH_SECURE placeholders is out of date; issue 29 removed secrets from shipped configuration entirely.

Co-Authored-By: Claude Opus 5 noreply@anthropic.com

Closes #3615511