feat(kad-dht): implement IPNS validator for DHT record validation

[asmit27rai]

Summary

Implement IPNS (InterPlanetary Naming System) validator for the Kademlia DHT, enabling py-libp2p to validate IPNS records according to the IPNS Record Specification.

IPNS provides mutable pointers to content-addressed data, essential for interoperability with IPFS nodes using go-libp2p and js-libp2p.

Changes

New Files

• libp2p/records/pb/ipns.proto - IPNS protobuf definition
• libp2p/records/pb/ipns_pb2.py - Generated protobuf code
• libp2p/records/pb/__init__.py - Package exports
• libp2p/records/ipns.py - IPNSValidator class implementation
• tests/core/records/test_ipns_validator.py - Comprehensive tests (19 cases)

Modified Files

• libp2p/kad_dht/kad_dht.py - DHT integration
• pyproject.toml - Added cbor2 dependency

Implementation Details

IPNSValidator validates records per IPNS spec §5.3:

1. Check record size ≤ 10 KiB
2. Parse protobuf, verify signatureV2 and data are present
3. Extract public key (from pubKey field or inlined Ed25519 in IPNS name)
4. Decode data as DAG-CBOR
5. Verify signature: pubkey.verify("ipns-signature:" + cbor_data, signatureV2)
6. Validate V1/V2 field consistency (if V1 fields present)
7. Check Validity expiration (RFC3339 timestamp with nanosecond support)

• Fixes: Implement IPNS validator for the Kademlia DHT #1157

[sumanjeet0012]

@asmit27rai Please fix the CI CD issues.

[yashksaini-coder]

@asmit27rai the lint ci nonetype errors are fixed, The pyrefly type checker wasn't properly narrowing the type of self.validator after the isinstance check, because instance attributes can theoretically be reassigned between the check and usage.

So I Assigned self.validator to a local variable after the type guard. This helps the type checker understand that the local variable validator is definitively a NamespacedValidator and cannot be modified, allowing safe access to _validators.

           # Use a local variable to help type checker narrow the type
            validator = self.validator
            
            # Add missing default validators
            if "pk" not in validator._validators:
                validator._validators["pk"] = PublicKeyValidator()
            if "ipns" not in validator._validators:
                validator._validators["ipns"] = IPNSValidator()

The last remaining ci check is not related to yours it is already addressed and I'm currently working on a fix for that, For more info read this discussion #1166

[asmit27rai]

@sumanjeet0012 You can review it.