feat(net): normalize inbound messages

[halibobo1205]

Summary

Add sanitize() to BlockCapsule and TransactionCapsule that normalizes the protobuf representation by stripping outer unknown fields, leaving all consensus-hashed and signed regions byte-identical.

Invocation:

• BlockMsgHandler.processMessage calls blockMessage.sanitize() after the existing size/time checks and before sync/adv dispatch. BlockMessage.sanitize() updates both the capsule and the message's wire data field (if it contains unknown fields).
• Manager.processTransaction calls trxCap.sanitize() after signature validation, only for mempool transactions (!trxCap.isInBlock()).
• Wallet.broadcastTransaction constructs the outbound TransactionMessage after pushTransaction so it reflects the post-sanitize state.

Each sanitize() short-circuits when there are no unknown fields, so the common path is allocation-free.

Compatibility

• Consensus state is unchanged.
• Existing size checks, error paths, response codes, and log lines are untouched.
• No consensus impact.