Move DecodedServiceEnvelope into its own file (#5715)

src/mqtt/ServiceEnvelope.cpp

@@ -0,0 +1,23 @@
+#include "ServiceEnvelope.h"
+#include "mesh-pb-constants.h"
+#include <pb_decode.h>
+
+DecodedServiceEnvelope::DecodedServiceEnvelope(const uint8_t *payload, size_t length)
+    : meshtastic_ServiceEnvelope(meshtastic_ServiceEnvelope_init_default),
+      validDecode(pb_decode_from_bytes(payload, length, &meshtastic_ServiceEnvelope_msg, this))
+{
+}
+
+DecodedServiceEnvelope::DecodedServiceEnvelope(DecodedServiceEnvelope &&other)
+    : meshtastic_ServiceEnvelope(meshtastic_ServiceEnvelope_init_zero), validDecode(other.validDecode)
+{
+    std::swap(packet, other.packet);
+    std::swap(channel_id, other.channel_id);
+    std::swap(gateway_id, other.gateway_id);
+}
+
+DecodedServiceEnvelope::~DecodedServiceEnvelope()
+{
+    if (validDecode)
+        pb_release(&meshtastic_ServiceEnvelope_msg, this);
+}