fix(token-usage): keep quiet-skipped passes free of the config lookup

The codex config.toml stat ran before the quiet-skip early return, so
no-op passes paid the codex-home walk for nothing; only lines fed to
the extractor consume the fallback speed. Also restores process_file's
doc comment (it had been orphaned onto the config helper) and orders
the config-fallback test's assertion by insertion order — both turns
share one 5-minute bucket, so ORDER BY bucket_ts rested on SQLite's
unspecified tie order.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>