Smooth camera animation

[slimbuck]

This PR:

• adds cubic (hermite) spline interpolation for camera movement from poses

Screen.Recording.2025-01-30.at.09.24.47.mov

Notes:

• with the new native project format (which stores camera poses) and camera interpolation, we can now:
  • offer the option of exporting animated movies
  • export camera spline to html viewer
  • improve the camera poses panel considerably
    • support multiple camera pose sets
    • transform pose sets with gizmos
    • support basic delete/insert/modify controls
    • display camera poses in the viewport
    • support selection of camera pose from 3d viewport
    • support for various camera input/export formats (especially nerfstudio format cc @simonbethke)
    • approximately another million things

[willeastcott]

This is great! I do wonder about whether cameras should be keyed on the timeline though. Undecided on that.

[slimbuck]

Ultimately a timeline would be the best. The camera pose panel builds the spline with consistent time steps, but the underlying spline implementation handles arbitrary times. So once we add timeline it should largely still just work.

[willeastcott]

Ultimately a timeline would be the best. The camera pose panel builds the spline with consistent time steps, but the underlying spline implementation handles arbitrary times. So once we add timeline it should largely still just work.

Then we can go with this but if there's time, consider squeezing in a very basic upgrade to our 4DGS timeline control. Let's see how things go over the next couple of days.