test(obs): replace source-text logging tests with logging guardrail script coverage
The seven fs::read_to_string source-text tests in crates/obs/src/logging.rs asserted retired logging patterns and required structured-logging fields across 13 files in other crates, four of them reverse reads into the rustfs binary crate. Their patterns are now enforced by scripts/check_logging_guardrails.sh, which runs in pre-commit and CI, covers the same files through checked_files plus require_patterns, and does not silently lapse when a governed file moves.
Part of rustfs/backlog#1884.
Zhengchao An