Add fuzz coverage for SV1 JSON-RPC messages

[0xjc65eth]

Summary

• add deserialize_sv1_json_rpc to fuzz arbitrary SV1 JSON-RPC bytes through serde and method parsing
• add roundtrip_sv1_messages to generate representative SV1 client/server messages and round-trip them through JSON-RPC parsing
• wire the sv1_api crate into the existing fuzz manifest

Closes #2124.

Testing

• cargo +1.89.0 check --manifest-path fuzz/Cargo.toml --bin deserialize_sv1_json_rpc --bin roundtrip_sv1_messages
• cargo +nightly fuzz run deserialize_sv1_json_rpc -- -max_total_time=5
• cargo +nightly fuzz run roundtrip_sv1_messages -- -max_total_time=5

late bytes still tell the truth.