Using retry_policy without max_retry_interval fails with no helpful error

[andystaples]

Calling context.call_activity with a retry policy that doesn't specify max_retry_interval prevents the retry behavior from working, causing the orchestration to fail after the first activity failure.
Example:

@bp.orchestration_trigger(context_name="context", orchestration="RetryActivityFunction")
def retry_activity_function(context: OrchestrationContext, _):
    retry_policy = RetryPolicy(
        first_retry_interval=timedelta(milliseconds=5000),
        max_number_of_attempts=3,
    )
    # raise_exception will throw on the first invocation, then succeed on the second
    yield context.call_activity('raise_exception', input=context.instance_id, retry_policy=retry_policy)
    return "Success"

Cause:
When the _OrchestrationExecutor runs process_event on the taskFailed event, it calls compute_next_delay on the task, which returns None because self._retry_policy.max_retry_interval is None. This shunts to the default "fail the orchestration" behavior without logging a reason why.

Not sure what the best solution is - should we have a default max_retry_interval, not enforce max_retry_interval if it is not specified, or continue to fail, but with a warning about providing max_retry_interval?