TensorFlow Federated 0.30.0

Release 0.30.0

Major Features and Improvements

• Add tests for namedtuples in the tff.program package.
• Add num_subrounds parameter to the mergeable context, allowing callers to
  optionally sequentialize subrounds.
• Add metrics support to tff.learning.models.FunctionalModel, including
  updates to the helper function create_functional_metric_fns and the
  downstream caller tff.learning.algorithms.build_weighted_fed_avg.

Bug Fixes

• Fix typo in the types constructed for testing the tff.program package.
• Fix some program example typos.
• Fix tests that don't seem to be running under the CI.
• Fix naming bug for Python mergeable execution.
• Ensure exceptions raised from remote executor stub implement gRPC error
  interface.
• Update tff.structure.Struct integration with JAX pytrees to not flatten
  the entire structure.
• Use Python 3.7 compatible type annotations until Colab updates to Python
  3.9.