Function redact_string 

pub fn redact_string(value: &str, policy: &RedactionPolicy) -> String

Apply redaction rules to a string value based on the given policy’s output level.

• None: returns the string unchanged.
• Baseline: wholesale-masks if the string matches any sensitive value prefix; otherwise applies entity detection and masks individual PII spans ([REDACTED:<category>]) while preserving surrounding context.
• Full: returns "[REDACTED]".