Adds a maintenance script that regenerates the S3-hosted PEP 503 simple index at:

https://mdb-build-public.s3.amazonaws.com/rapidyaml_wheels/simple/

so each anchor carries a `#sha256=<hex>` fragment. Standalone tool that runs on demand after uploading a new rapidyaml wheel or sdist to the bucket.

This tooling landing separately is a prerequisite for the uv and pycross migration PR.