chore(ci): add bump_msrv.py script

[dannycjones]

Which issue does this PR close?

N/A

What changes are included in this PR?

I authored this script (with the assistance of an LLM) to make MSRV version bumps simple.

Are these changes tested?

Yes, I used it to author this PR: #2652

I have tested it with and without a GITHUB_TOKEN and validated the error handling worked for throttling.

[blackmwk]

I'm hesitating adding this script, upgrading rust toolchain and msrv is just one line change and a simple lookup, there is no need to automate this with maintaining burden.

[dannycjones]

I'm hesitating adding this script, upgrading rust toolchain and msrv is just one line change and a simple lookup, there is no need to automate this with maintaining burden.

I share the hesitation. The script ended up being longer than expecting (and easy for GenAI to churn out) for minimal gain. It only skips the manual process of browsing the release page and picking out a good version matching the criteria.

The flip side (why I tried writing it) was to be able to add a simple script to run in the release guide and/or whenever someone wants to update MSRV. It'll cover not just the Cargo.toml but also the Rust toolchain used by clippy, etc.

I'm happy to close it, unless someone wants to include it.