test(cli): cover rm purge option defaults

[overtrue]

Summary

This adds focused unit coverage for the request-option mapping behind the recent rm --purge work.

The merged change in #82 introduced delete_request_options so the CLI can opt into RustFS force-delete semantics, but the unit tests only exercised the positive purge = true branch. That left the default branch and the easy-to-confuse force = true, purge = false branch unverified.

Root cause

Recent follow-up PRs already covered --purge help and parser wiring, plus the S3 client header behavior. The small helper in crates/cli/src/commands/rm.rs still had a gap around the non-purge paths that feed those lower-level calls.

Fix

The test module now adds two narrow assertions:

• default remove options keep force_delete disabled;
• --force alone does not enable force_delete unless --purge is also set.

This keeps the scope limited to the recent rm change surface and avoids production code changes.

Validation

I ran these successfully:

• cargo test -p rustfs-cli delete_request_options --lib
• cargo fmt --all --check
• cargo clippy --workspace -- -D warnings
• cargo test --workspace

I also ran make pre-commit per the automation instructions, but this checkout does not define that target, so make exits with No rule to make target 'pre-commit'.