Table list caching Partition class

[codeactual]

Currently a ‘tablelist’ group key is invalidated at the end of methods like
createTable() and dropTable(), which at first seems excessive. But then
they do allow all getTableLike() caches to be invalidated when we don’t
know which of them should now, or does now, contain the created/dropped
table in question.

In any case, the Partition class’ cache use seems sub-optimal in general
should probably get some more eyes on it.

Filing this under Design since there isn’t a certain issue yet.

[codeactual]

Reminder: Methods like createTable() do not seed values of keys like tableExists()’s,
so the first lookup always misses.