v1.21.0

attestation.verify() — the consumer half of the envelope. v1.20.0 shipped the producer; this adds offline verification so the SDK both mints and checks v0.1.1 attestation envelopes in one place.

• verify(envelope, *, now=None) -> VerificationResult runs the deterministic, network-free subset of the spec's verifier: structural checks (required fields, envelope_version, non-empty evidence/sigchain) → ed25519 peel-and-verify of each signature over JCS(envelope with sigchain = sigchain[0..i-1]) → validity window (time_bounded/perpetual/revocation_checked) → issuer did:key binding.
• VerificationResult carries ok (truthy via __bool__), issuer_bound (kept separate — only did:key issuers close cryptographically in v0.1; other schemes are valid-but-UNBINDABLE), reasons, and notes.
• did_key_to_public_key() — inverse of public_key_to_did_key().

Evidence resolution and revocation are intentionally out of scope — verify() never makes a network call; resolve evidence[].uri / check content_hash / query revocation_uri yourself if your trust model needs them. Same optional extra as signing (pip install colony-sdk[attestation]). Non-breaking, additive.