Move region search methods. Remove skymap methods.

[delucchi-cmu]

Move all region _search methods from Catalog to HealpixDataset, as they are all possible for anything with spatial data.

Closes #523

Removes the skymap_data and skymap_histogram methods.

[github-actions]

Before [a64e4f8]	After [0578cdf]	Ratio	Benchmark (Parameter)
40.4±0.8ms	40.7±0.8ms	1.01	benchmarks.time_polygon_search
83.0±1ms	82.2±1ms	0.99	benchmarks.time_kdtree_crossmatch
6.47±0.03s	6.36±0.01s	0.98	benchmarks.time_create_large_catalog
967±10ms	952±5ms	0.98	benchmarks.time_create_midsize_catalog
25.8±0.2ms	24.3±0.3ms	0.94	benchmarks.time_box_filter_on_partition

Click here to view all benchmarks.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.14%. Comparing base (a64e4f8) to head (7bbe890).
⚠️ Report is 122 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #960      +/-   ##
==========================================
- Coverage   95.26%   95.14%   -0.13%     
==========================================
  Files          55       54       -1     
  Lines        2598     2531      -67     
==========================================
- Hits         2475     2408      -67     
  Misses        123      123              

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[dougbrn]

Looks good!