Support map_partitions ufunc with non data frame output

[smcguire-cmu]

Currently if the user returns a non data frame when calling map_partitions (e.g. returning a series) it uses this as the ddf in another catalog, which causes errors when the catalog expects a ddf but actually gets a series.

This updates the map_partitions method to check that the return type is a data frame. If the return type isn't, the raw dask collection is returned instead of creating the catalog.

Fixes #324

[github-actions]

Before [73948db]	After [42e3993]	Ratio	Benchmark (Parameter)
6.51±0.4ms	6.92±0.3ms	1.06	benchmarks.time_box_filter_on_partition
15.0±0.7ms	15.3±0.4ms	1.02	benchmarks.time_polygon_search
468±5ms	471±2ms	1.01	benchmarks.time_create_midsize_catalog
48.3±0.7ms	48.9±0.4ms	1.01	benchmarks.time_kdtree_crossmatch
3.16±0.01s	3.17±0.02s	1	benchmarks.time_create_large_catalog

Click here to view all benchmarks.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.31%. Comparing base (6ac42b6) to head (b329cd4).
Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #357   +/-   ##
=======================================
  Coverage   98.30%   98.31%           
=======================================
  Files          43       43           
  Lines        1418     1421    +3     
=======================================
+ Hits         1394     1397    +3     
  Misses         24       24           

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