Add MsgPack format support - #1068

Summary

• Adds msgpack as a first-class Arroyo Format, including SQL connector options and OpenAPI/client type exposure.
• Implements MsgPack source deserialization for structured map records and into_unstructured_json payloads.
• Implements MsgPack sink serialization, including native MsgPack binary values for Arrow binary fields.
• Wires Kafka schema validation and format/schema validation coverage for the new format.

Notes

• Structured MsgPack records are decoded through Arroyo's existing Arrow JSON path, so top-level records must be MsgPack maps with string keys.
• MsgPack extension values are currently rejected instead of silently lossy-converted.

Testing

• cargo fmt --check
• cargo test -p arroyo-formats
• cargo test -p arroyo-rpc msgpack
• cargo check -p arroyo-connectors -p arroyo-planner -p arroyo-formats -p arroyo-rpc
• cargo check -p arroyo-api with a temporary local Postgres database for compile-time SQL validation
• pnpm run openapi
• pnpm exec tsc --noEmit
• pnpm run build

Fixes #904