Expose NT entry change time in PhotonLib (#562)

Adds target change timestamp to PhotonPipelineResult

Co-authored-by: Matt <matthew.morley.ca@gmail.com>

photon-lib/src/main/java/org/photonvision/PhotonCamera.java

@@ -102,9 +102,14 @@ public class PhotonCamera {
 
         // Populate packet and create result.
         packet.setData(rawBytesEntry.getRaw(new byte[] {}));
+
         if (packet.getSize() < 1) return ret;
         ret.createFromPacket(packet);
 
+        // Set the timestamp of the result.
+        // getLatestChange returns in microseconds so we divide by 1e6 to convert to seconds.
+        ret.setTimestampSeconds((rawBytesEntry.getLastChange() / 1e6) - ret.getLatencyMillis() / 1e3);
+
         // Return result.
         return ret;
     }