Scope RustFS CI to relevant changes

[aaltshuler]

Summary

• classify RustFS S3 integration separately from the general workspace test job
• only run RustFS CI on main pushes, tags, manual dispatch, or PRs that touch RustFS/S3-sensitive files
• split the RustFS cargo commands into named steps and raise the job timeout so future logs are clearer when the job does run

Root cause

The RustFS job was not hanging in a test. The previous cancelled run spent most of its 45 minute budget compiling the RustFS test targets, then got cancelled before the CLI smoke finished compiling.

Verification

• reviewed the cancelled RustFS job log from run 24287260896
• simulated the new classifier logic locally for PR Implement aggregate functions with GROUP BY support #6 changed files (, )