Return proper error for empty address

[chenyukang]

fnn-cli connect_peer --address "" expect to return error here:

https://github.com/nervosnetwork/fiber/blob/b77a07dd45b06aeb0a3c894bf9a533d9d568ee63/crates/fiber-lib/src/rpc/peer.rs#L64

[Copilot]

Pull request overview

This PR fixes parsing of empty or whitespace-only multiaddr strings to properly return an error instead of creating an invalid empty Multiaddr. The issue was triggered by fnn-cli connect_peer --address "" which should return an error.

Changes:

• Added a check in Multiaddr::from_str to return Error::InvalidMultiaddr when parsing produces no protocol bytes
• Added test coverage for empty (""), whitespace (" "), and slash-only ("/") inputs

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.