Add a Python port of the KEZ CLI under python/, mirroring the Rust and
Node implementations command-for-command and byte-for-byte:
- Pure-Python JCS (RFC 8785), BIP-340 Schnorr, and Bech32; cryptography
for Ed25519 and zstandard for the compact zstd framing.
- Full CLI: identity new, claim create/dns, verify file, and
sigchain add/revoke/show/export.
Wire Python into crosstest.sh with 35 new scenarios covering Python
against both Rust and Node, in every direction, across all wire formats,
both key types, DNS proofs, and sigchains (incl. JSONL byte parity).
All 55 scenarios pass.
Update root README and .gitignore for the new implementation.
