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.
Sort is here because I'm assuming the order of elements returned from calling seq on a map or set is not guaranteed. If it is then a) this can be removed b) PersistentUnrolledMap has a bug