Implement BLE MAC address randomization for privacy

[BigNathan1]

Implement BLE MAC address randomization for privacy

closes #38

Adds privacy enhancement through BLE Central MAC address rotation to prevent passive location tracking. This implementation defines the interface and rotation policy for both simulation and future Android JNI binding.

Changes:

• Added MacAddressProvider trait and RandomMacProvider implementation for injectable MAC address generation with locally-administered bit set
• Enhanced BleCentral with MAC rotation state management including rotate_mac_if_due() method with configurable 15-minute default interval
• Added TopologyFlag::MacRotated variant to signal MAC rotation events to connected peers via topology updates
• Implemented TransportManager.notify_mac_rotated() to drop all BLE connections after rotation (WiFi-Direct connections unaffected)
• Integrated MAC rotation check into power_tick_at() to emit MacRotated flag on rotation

Implementation Details:

• RandomMacProvider generates random 6-byte MAC addresses with locally-administered bit set (bit 1 of byte 0)
• BleCentral tracks last rotation timestamp and checks if interval has elapsed before generating new MAC
• Upon rotation, all BLE connections are dropped as they reference the old MAC address
• New MAC address is broadcast to peers via TopologyFlag::MacRotated for peer re-discovery
• Comprehensive test coverage including:
  • 1000 random MAC generations verify locally-administered bit compliance
  • Rotation timing and double-rotation prevention tests
  • BLE connection cleanup while preserving WiFi-Direct connections
  • Power tick integration with MacRotated flag in topology updates

Acceptance Criteria Met:

• RandomMacProvider::generate() always sets locally-administered bit and clears multicast bit
• BleCentral::rotate_mac_if_due() returns None before interval and Some(new_mac) after
• No double-rotation: consecutive immediate calls return None after first rotation
• TopologyFlag::MacRotated included in PowerTickOutcome::topology_flags on rotation
• BLE connections dropped after notify_mac_rotated() call
• WiFi-Direct connections survive MAC rotation
• Full test suite coverage for BLE transport module