Major Features and Improvements
* Updated the type annotation for the `dtype` parameter to `tff.TensorType`.
* Added adaptive tuning function to `ThresholdSampling` class.
* Added
`tff.learning.models.ReconstructionModel.from_keras_model_and_variables`,
which provides a way to get a `ReconstructionModel` from a Keras model and
lists of global and local trainable/non_trainable *variables*.
* Switched `tff.learning.algorithms.build_fed_recon_eval` to use a stateful
metrics aggregator.
Breaking Changes
* Removed `tff.learning.models.ReconstructionModel.from_keras_model`, which
has been replaced by
`tff.learning.models.ReconstructionModel.from_keras_model_and_layers`.
* Removed the following functions from the py_typecheck module: `check_len`,
`check_callable`, `is_dataclass`,`is_attrs`, `check_subclass` and
`check_not_none`. They are unused or can be replaced by Python type
annotations.
Bug Fixes
* Fixed a small bug in the TFF SGDM optimizer, to only track momentum as a
hparam if it is both specified and nonzero.