Kwcoco

Added
* Initial non-experimental version of SensorChanSpec with limited functionality
* Updated `kwcoco validate` cli tool with full options (and added checks for img attrs)
* New Delayed operations with a more scalable design

Fixed
* Fix compatibility issue with datasets that do not contain an annotations list
* Issue where the original coco polygons did not validate correctly in the schema.
* The new delayed operations now always return an arraylike

Changed
* FusedChannelSpec now has an `__eq__` method that returns True if the parsed reprs are the same.

Changed
* kwcoco subset can now accept dst as the second positional argument

Fixed
* Fix issue in kwcoco subset where paths were invalid if written outside of
the source kwcoco bundle.

Added
* kwcoco validate now accepts `--require_relative` which causes non-portable
kwcoco files with non-relative paths to fail.
* kwcoco validate now checks for duplicate bands in the auxiliary dictionary.

Changed
* Better verbosity for demodata
* Experimental support for ujson
* Remove deprecated usage of cfgstr with ubelt.Cacher
* kwcoco stats output is modified

Fixed
* CocoImage Affine transform `matrix` attribute is now always populated.

Changed
* CocoDataset.dump now uses `safer` with `temp_file=True` by default.
* Initial steps to rename "auxiliary" to "assets" in a backwards compatible way.