Add regression test asserting Settings debug output excludes secret values

[ChristianPavilonis]

Context

PR #468 introduced Redacted<T> to wrap secret fields in Settings so they print [REDACTED] in debug/display output. However, there is no test that enforces this across all secret-bearing fields. If a future field is added without wrapping in Redacted<T>, there is no safety net to catch the leak.

Proposal

Add a test that:

1. Constructs a Settings instance with known secret values (e.g. "CANARY_SECRET")
2. Formats it with format!("{:?}", settings)
3. Asserts the output does not contain the canary strings
4. Asserts the output does contain [REDACTED]

This ensures any future secret field that forgets Redacted<T> is caught at test time.

References

• PR Redact secrets from logs and downgrade PII log levels #468 review: Redact secrets from logs and downgrade PII log levels #468 (review)