TensorFlow Federated 0.51.0

Release 0.51.0

Major Features and Improvements

• Enabled, improved, and fixed Python type annotations in some modules.
• Added the interface of loss_fn to tff.learning.models.FunctionalModel,
  along with serialization and deserialization methods.
• Updated the composing executor to forward the type field of Intrinsic
  protos that are sent to child executors.
• Added an executor binding for DTensor based executor.

Breaking Changes

• Deprecated tff.framework.DataBackend. Python execution is deprecated
  instead use CPP Execution.

Bug Fixes

• Fixed the formulation of the JIT constructed mapped selection computation
  that is sent to the remote machine in streaming mode.
• Fixed the usage of np.bytes_ types that incorrectly truncate byte string
  with null terminator.