Production panic points in WebSocket subscription handlers

[qj0r9j0vc2]

Multiple .unwrap() calls in WebSocket subscription handlers can cause panics in production.

Locations:

• https://github.com/decipherhub/cipherbft/blob/main/crates/rpc/src/pubsub.rs#L298
• https://github.com/decipherhub/cipherbft/blob/main/crates/rpc/src/pubsub.rs#L335
• https://github.com/decipherhub/cipherbft/blob/main/crates/rpc/src/pubsub.rs#L373
• https://github.com/decipherhub/cipherbft/blob/main/crates/rpc/src/pubsub.rs#L408
• https://github.com/decipherhub/cipherbft/blob/main/crates/rpc/src/pubsub.rs#L446

All are SubscriptionMessage::from_json(&msg).unwrap() calls that can panic on serialization failure.