fix(python): TrackableState: only invoke callbacks on actual change
fix(python): TrackableState: only invoke callbacks on actual change

google/neuroglancer,janelia-flyem/neuroglancer,seung-lab/neuroglancer,google/neuroglancer,google/neuroglancer,janelia-flyem/neuroglancer,janelia-flyem/neuroglancer,seung-lab/neuroglancer,janelia-flyem/neuroglancer,seung-lab/neuroglancer,seung-lab/neuroglancer,google/neuroglancer,janelia-flyem/neuroglancer,google/neuroglancer,seung-lab/neuroglancer,seung-lab/neuroglancer,google/neuroglancer,google/neuroglancer,seung-lab/neuroglancer,google/neuroglancer