test(cli): cover malformed cors bucket paths

[overtrue]

Summary

This change closes a small test gap in the recent bucket CORS path validation work. The CORS parser normalized a trailing slash, but it still accepted malformed bucket paths such as alias//bucket and alias/bucket/nested, which do not match the documented alias/bucket contract.

Root cause

parse_bucket_path only rejected an empty normalized bucket segment. Any remaining slash inside the bucket portion survived validation and was treated as part of the bucket name.

Fix

The parser now rejects normalized bucket segments that still contain /, and the existing error-path unit test now covers both malformed inputs.

Validation

I attempted make pre-commit first, but this repository does not define that target or a Makefile. I then ran the documented equivalent checks directly:

• cargo fmt --all --check
• cargo clippy --workspace -- -D warnings
• cargo test --workspace