test(cli): reject object paths for ilm rules

[overtrue]

Summary

This PR closes a small lifecycle command test gap in the ILM rule bucket path parser.

The ilm rule commands document bucket paths as alias/bucket, but the parser previously split at the first slash and accepted paths such as local/my-bucket/key.txt. That treated my-bucket/key.txt as the bucket name, so an object-style path could get past local validation and fail later as a confusing bucket lookup or backend request.

The fix keeps trailing slashes valid for bucket paths while rejecting any non-empty path segments after the bucket. The added regression assertions cover both one-segment and nested object keys.

Validation

• cargo test -p rustfs-cli commands::ilm::rule::tests::test_parse_bucket_path_error
• cargo fmt --all --check
• cargo clippy --workspace -- -D warnings
• cargo test --workspace

make pre-commit was requested, but this repository checkout has no Makefile and no pre-commit target, so it could not be run.