feat(gossip): implement epidemic broadcast fanout in run_gossip_loop (#82)

[ZuLu0890]

Summary

Closes #82.

Implements the epidemic broadcast fanout logic in run_gossip_loop that was previously stubbed with a TODO.

Changes

src/gossip/protocol.rs

• run_gossip_loop now accepts state: Arc<Mutex<GossipState>> as a parameter
• Epidemic push fanout: on each round tick, drains buffered messages from the active queue, calculates fanout target via FanoutCalculator (logarithmic scaling, clamped to MIN/MAX), selects a random peer subset with select_random_peers, and sends each message to each selected peer
• Also moves a paced recovery batch from the macro-merge backlog on each tick
• Anti-entropy pull: on the 30-second tick, picks one random peer and sends a SyncRequest built from the current GossipState
• Updated unit tests to pass the new GossipState argument

src/gossip/fanout.rs

• Added FanoutCalculator::calculate_target(active) — simplified API delegating to calculate(active, None)
• Added FanoutCalculator::select_random<T: Clone>(&self, items, f) — generic peer selection (used by integration tests)

src/gossip/bloom.rs

• Added BloomFilter — a public two-window sliding bloom filter with a &[u8] API, matching the type expected by tests/gossip_test.rs

src/gossip/round.rs

• Added RoundScheduler — a public wrapper around GossipScheduler with get_interval() and advance_time(delta) for integration test use

tests/message_format_validation_test.rs

• Fixed pre-existing compile error: added missing topology_flags: vec![] to TopologyUpdate initializer

Tests

• ✅ 9 gossip integration tests (cargo test --test gossip_test)
• ✅ 33 gossip unit tests (cargo test --lib gossip)
• Pre-existing failures in topology_test and relay_node_submission are unaffected by this PR (confirmed on main before changes)

[Mrwicks00]

@ZuLu0890 fix cicd error