feat(discovery): implement BLE scanner and advertiser

[Favour4712]

feat(discovery): Implement BLE Peer Scanner and Advertiser

Closes #23

Description

This PR implements the BLE discovery layer in src/discovery/ble.rs.

Changes

• BleAdvertisementPayload: 33-byte struct (32-byte pubkey + 1-byte caps). Encodes/decodes the manufacturer data payload embedded in BLE advertisements. Capability flags: bit 0 = is_relay, bit 1 = has_wifi_direct.
• BleScanner: Holds an Arc<Mutex<PeerList>> and a broadcast::Sender<DiscoveryEvent>. The testable handle_advertisement() method decodes the payload, calls PeerList::insert_or_update (using the advertisement RSSI as signal_strength), and broadcasts the resulting DiscoveryEvent to all subscribers. The start() / stop() stubs hook into the btleplug scan loop in production.
• BleAdvertiser: Encodes the local PeerIdentity into a BleAdvertisementPayload and begins advertising with SC_SERVICE_UUID. The build_payload() method is testable without hardware.
• Added #[derive(Clone)] to DiscoveryEvent to satisfy the broadcast::Sender<T> bound.
• Fixed a pre-existing flaky assertion in the bloom filter rotation test that was incorrectly asserting false on probabilistic bloom filter membership checks.

Platform Note: btleplug requires a real or virtual BLE adapter for integration tests. Unit tests cover all pure Rust logic.

[grantfox-oss]

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@BigNathan1's PR #144 was approved and merged by @Mrwicks00.

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👏 Great work, @BigNathan1! Keep contributing to StellarConduit.