Refactor per-model unit testing (#1083)
* Set up per-model unit tests
* Rename tests
* Do not modify original object when updating model file name
* Distribute unit tests across separate files
* Update comments
* Update tokenization test file names
* Refactor: use asset cache
* Destructuring for code deduplication
* Remove empty file
* Rename deberta-v2 -> deberta_v2
* Rename
* Support casting between number and bigint types
* Use fp32 tiny models
* Move image processing tests to separate folders + auto-detection
