Write point map with cdshealpix skymap

[camposandro]

Migrate the point_map.fits I/O operations to use cdshealpix skymap methods. Closes #399.

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 92.89%. Comparing base (8e1d456) to head (37f3b9d).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #409      +/-   ##
==========================================
+ Coverage   92.69%   92.89%   +0.19%     
==========================================
  Files          49       49              
  Lines        2095     2096       +1     
==========================================
+ Hits         1942     1947       +5     
+ Misses        153      149       -4     

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[github-actions]

Before [8e1d456]	After [c35593e]	Ratio	Benchmark (Parameter)
13.9±0.9ms	15.0±1ms	1.08	benchmarks.Suite.time_inner_pixel_alignment
1.01±0.03ms	1.05±0.03ms	1.04	benchmarks.time_test_cone_filter_multiple_order
110±1ms	112±1ms	1.02	benchmarks.Suite.time_paths_creation
94.3±0.5ms	94.4±0.7ms	1	benchmarks.MetadataSuite.time_load_partition_join_info
387±0.9ms	387±3ms	1	benchmarks.Suite.time_outer_pixel_alignment
23.0±0.3ms	22.9±0.2ms	0.99	benchmarks.MetadataSuite.time_load_partition_info_order6
46.3±0.4ms	45.8±0.2ms	0.99	benchmarks.Suite.time_pixel_tree_creation
125±0.6ms	124±0.3ms	0.99	benchmarks.time_test_alignment_even_sky
95.5±0.3ms	93.9±0.8ms	0.98	benchmarks.MetadataSuite.time_load_partition_info_order7

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