Add 7 new modules with all core data types for the mesh routing protocol:
- tree.rs: ParentDeclaration, TreeCoordinate, TreeState
- bloom.rs: BloomFilter (4KB/7 hash), BloomState with debouncing
- transport.rs: TransportId, LinkId, Link, Transport trait, LinkStats
- protocol.rs: Auth messages, TreeAnnounce, FilterAnnounce, LookupRequest/Response, SessionSetup, DataPacket
- cache.rs: CoordCache, RouteCache with LRU eviction and TTL expiry
- peer.rs: Peer lifecycle states, filter tracking, UpstreamPeer
- node.rs: Node container with resource limits
All entities have constructors, error types, and comprehensive tests (161 total).
Stub methods with todo!() for behavior to be implemented later.
No state machine logic, protocol handlers, or async code yet.
