feat(consensus): Add stake-based governance with bootstrap period

Implements a sophisticated governance system for chain modifications:

- 50%+ stake threshold required for consensus after bootstrap
- Bootstrap period (block < 7,175,360) allows subnet owner to execute
  actions without stake verification while validators join
- Owner hotkey: 5GziQCcRpN8NCJktX343brnfuVe3w6gUYieeStXPD1Dag2At

Security features:
- Proposal system with timeout (24h) and min voting period (1h)
- Double-voting prevention
- Rate limiting (max 10 proposals/day/validator)
- Signature verification on all votes
- BootstrapSyncPolicy for trusted sync during bootstrap

New modules:
- stake_governance.rs: Core governance engine
- governance_integration.rs: PBFT and metagraph integration

Also adds:
- RateLimited error type in core/error.rs
- sign_bytes() method in core/crypto.rs

Author: EchoBT

Cargo.lock

@@ -12,6 +12,7 @@ async-trait = { workspace = true }
 
 serde = { workspace = true }
 serde_json = { workspace = true }
+bincode = { workspace = true }
 
 tracing = { workspace = true }
 anyhow = { workspace = true }