Revert part of some breaking changes in using rate_per_task_name

PiperOrigin-RevId: 596903315

seqio/experimental.py

@@ -206,7 +206,7 @@ def add_fully_cached_mixture(
   return MixtureRegistry.add(
       new_name,
       [
-          (new_t.name, mixture.rate_per_task_name[old_t.name])
+          (new_t.name, mixture._task_to_rate[old_t.name])  # pylint:disable=protected-access
           for old_t, new_t in zip(mixture.tasks, new_tasks)
       ],
   )

seqio/helpers.py

@@ -146,7 +146,7 @@ def _validate_output_features(og_output_features, new_output_features):
   # This is a Mixture. Create and register new sub-Tasks/Mixtures with the
   # provided vocab/output_features, then create a new Mixture.
   new_tasks_and_rates = []
-  for task_name, rate in mixture_or_task.rate_per_task_name.items():
+  for task_name, rate in mixture_or_task._task_to_rate.items():
     new_task_name = f"{new_mixture_or_task_name}.{task_name}"
     new_task = mixture_or_task_with_new_vocab(
         task_name,
@@ -306,7 +306,7 @@ def mixture_or_task_with_truncated_data(
     # This is a Mixture. Create and register new sub-Tasks/Mixtures with the
     # provided vocab/output_features, then create a new Mixture.
     new_tasks_and_rates = []
-    for task_name, rate in mixture_or_task.rate_per_task_name.items():
+    for task_name, rate in mixture_or_task._task_to_rate.items():
       new_task = mixture_or_task_with_truncated_data(
           task_name,
           f"{new_mixture_or_task_name}.{task_name}",
@@ -354,7 +354,7 @@ def mixture_with_missing_task_splits_removed(
   """
   og_mix: dp.Mixture = dp.get_mixture_or_task(mixture_name)  # pytype: disable=annotation-type-mismatch  # always-use-return-annotations
   new_tasks_and_rates = []
-  for task_name, rate in og_mix.rate_per_task_name.items():
+  for task_name, rate in og_mix._task_to_rate.items():
     subtask: dp.Task = dp.get_mixture_or_task(task_name)  # pytype: disable=annotation-type-mismatch  # always-use-return-annotations
     if split in subtask.splits:
       new_tasks_and_rates.append((subtask.name, rate))