* Initial submit
* Fix bugs:
1. add __init__ file
2. tied word embedding
3. support flash/flex attention
4. model saving and loading
* Code refactor:
* Rename encdecgemma to t5gemma.
* Split attention into self- and cross-attention
* Split stack into encoder and decoder
* Add test cases
* Add auto configuration
* Update configurations.
* Fix bugs related to copy and attribute checks
* Fix type union
* Fix merge errors
* run ruff format
* Run make style and update tests.
* Add t5gemma model doc.
* ruff and style formatting.
* Add missed module config.
* Add dummy checkpoint link to pass tests (need updated when real checkpoints are uplioaded.).
* Update model doc.
* Minor updates following Arthur's comments:
* replace docstrings with auto_docstrings
* remove checkpoint layers
* remove deprecate_kwargs
* fix rebase errors
* Fix docstring issues.
* fix t5gemma doc issue.
* run ruff format
* Updates:
* split encoder-only model out
* make t5gemmamodel encoder-decoder only
* update token and sequence classification
* update tests
