Add basic ERT (OOK) utility meter reception.

Extracted the Manchester formatting function for use in ERT, now also returns an indication of bits in error.

firmware/common/message.hpp

@@ -46,6 +46,7 @@ public:
 		TPMSPacket = 6,
 		Shutdown = 8,
 		AISPacket = 7,
+		ERTPacket = 9,
 		MAX
 	};
 
@@ -240,6 +241,22 @@ public:
 	}
 };
 
+struct ERTPacket {
+	uint64_t preamble { 0 };
+	std::bitset<1024> payload;
+	size_t bits_received { 0 };
+};
+
+class ERTPacketMessage : public Message {
+public:
+	constexpr ERTPacketMessage(
+	) : Message { ID::ERTPacket }
+	{
+	}
+
+	ERTPacket packet;
+};
+
 class MessageHandlerMap {
 public:
 	using MessageHandler = std::function<void(Message* const p)>;