Refactor: BitchatMessage (#610)

* Extract BitchatMessage into a separate file

* Convert `fromBinaryPayload` to `convenience init?`

* Extract message dedup into an extension

* Remove dead `formatMessageContent`

* Minor refactor of timestamp and username formatting

* Remove dead `getSenderColor`

bitchatTests/Mocks/MockBLEService.swift

@@ -309,7 +309,7 @@ final class MockBLEService: NSObject {
 
     func simulateIncomingPacket(_ packet: BitchatPacket) {
         // Process through the actual handling logic
-        if let message = BitchatMessage.fromBinaryPayload(packet.payload) {
+        if let message = BitchatMessage(packet.payload) {
             var shouldDeliver = false
             seenLock.lock()
             if !seenMessageIDs.contains(message.id) {