Zephir

New:
* COMMAND: 'auto_annotate' for automatically annotating a select frame with no linking
* COMMAND: 'train_zephod' for training a ZephOD model

Updated:
* fixed a bug where k_ij could not be properly constructed when nn_max=0
* ZephOD training updated to handle multiple datasets
* ZephOD training updated wth autocast and gradient scaling
* fixed a bug where some ZephOD channel could not process volumes with many z-slices
* fixed a bug where apply_255_lut() could result in NaN's
* fixed a bug where datasets scaled 0-1 was not properly rescaled for ZephOD ops

New:
- using `lr_coef <= 0` skips all distance calculations and sets initial learning rate at `lr_floor` regardless of distance to parent

Updated:
- using `sort_mode = linear` builds a partial distance matrix instead of a full one to streamline calculations
- using `sort_mode = linear` assigns the root of a branch as the reference frame instead of the closest reference frame (previous behavior)
- `methods/save_movie` places data in the right channel in the movie when using `channel`
- fixed a bug where parent frames were improperly assigned when using `sort_mode = linear` with multiple sequential frames in `t_ignore`
- fixed a bug where `update_frame` macro did not recompile correctly when using `t_track`

New:
- **OPTION**: `t_track` specifies a list of frames to analyze; supercedes existing option `t_ignore`

Updated:
- `methods/save_movie` only saves reference frames and tracked frames
- `methods/save_movie` saves all available frames (previous behavior) when `include_all=True`
- `docs/Guide-ZephIR` updated with tips on `t_track`

Preprint release.