test(sql): cover select error exit codes

[overtrue]

Related issue(s)

Automated test-gap detection for the recent S3 Select command work.

Background

The S3 Select command recently added command-level handling for backend errors returned by the select adapter. Existing and open coverage now exercises parser wiring and S3 serialization shapes, but the SQL command's final mapping from rc-core errors to CLI exit codes was not directly covered.

Root cause

sql::execute delegates backend failures through exit_code_from_error, so regressions in unsupported-feature, missing-object, auth, network, or generic error mappings could change automation-visible process outcomes without a focused command-layer test.

Solution

Add a small unit test in crates/cli/src/commands/sql.rs that covers representative backend errors and their expected SQL command exit codes. This keeps the scope limited to the recent S3 Select command path and avoids duplicating the open parser and S3 serialization PRs.

Test status

• cargo test -p rustfs-cli commands::sql::tests::sql_exit_code_from_backend_errors --lib
• cargo fmt --all --check
• make pre-commit