Validate P2P bytes before serializing multiaddrs

[Officeyutong]

Summary

• validate Protocol::P2P bytes before writing them into a Multiaddr
• prevent safe construction APIs from creating internally invalid multiaddrs
• add regression tests for Multiaddr::from, push, and FromIterator

Rationale

Protocol::P2P is publicly constructible from raw bytes. Parsers already validate P2P bytes, but construction paths serialized them directly, allowing invalid internal Multiaddr values that could later panic during iteration or display.

This keeps the existing API shape while enforcing the same P2P invariant at serialization time.

Tests

• cargo fmt --check
• cargo test -p tentacle-multiaddr -- --nocapture

[Copilot]

Pull request overview

This PR enforces Protocol::P2P byte invariants at serialization time so that Multiaddr construction APIs (from, push, FromIterator) can’t produce internally invalid multiaddrs that may later panic during iteration/display.

Changes:

• Add Protocol::P2P validation (check_p2p) inside Protocol::write_to_bytes before encoding into a multiaddr.
• Add regression tests asserting invalid Protocol::P2P bytes are rejected (panic) via Multiaddr::from, push, and collect.
• Add a positive regression test confirming valid P2P construction paths continue to work.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
multiaddr/src/protocol.rs	Validates Protocol::P2P bytes before encoding, preventing invalid Multiaddr byte representations from being created via serialization.
multiaddr/tests/lib.rs	Adds regression coverage for invalid/valid P2P behavior across key construction APIs.

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