DMARC: pct= tag not enforced

[Jaro-c]

RFC 7489 §6.6.2 requires that messages outside the pct= percentile be treated as if policy were none, effectively downgrading enforcement. Currently pct= is parsed but silently discarded — every failing message is rejected/quarantined regardless of the percentage.

Fix: parse pct= into Record, apply sampling in evaluate() via ring::rand::SystemRandom. Non-numeric values are a parse error (permerror).

[Jaro-c]

Fixed by PR #104: pct= enforced in DMARC evaluation with RNG sampling.