fuzz test some simple sequence actions

maps, vectors, and sets can all be converted to seqs, and often carry their own seq implementations. Fuzz-test those.

This should provide the same coverage as #5 but through generation rather than through special-casing.
Order is not guaranteed, but neither is the fact that entries are comparable and can be sorted.  This can probably be inferred by creating some sample keys and values and seeing if they can be sorted, but just setting `sort?` to true in `assert-map-like` isn't valid.