Admin client impl fixes

[siobhan-sterrett]

A handful of minor fixes to cimpl. Probably nothing that will impact real-life use-cases, since these are all buried inside _AdminClientImpl, but they were bothering me.

1. Swaps "topic_names" and "future" in kws array in Admin_describe_topics()

If a user tried to pass topic_names or future into _AdminClientImpl.describe_topics() as keyword arguments, they would end up swapped, which would lead to confusing errors.

2. Raises TypeError in Admin_list_consumer_group_offset() if request is not a list
3. Raises TypeError in Admin_alter_consumer_group_offsets() if request is not a list

In both of these cases, the library would raise ValueError if request was a list with anything other than 1 item... but if request wasn't a list, it would result in an internal error when it tried to access its first item.

4. Allows elements of plist in py_to_c_parts() to be instances of a subtype of TopicPartition

If a user passed a list of instances of a subtype of TopicPartition, the library would raise a TypeError, even if the instances were otherwise valid.

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[joaoe]

I think this might touch some code I changed here
#1591

But this project is not accepting PRs. It's annoying.