Simplify catalog reading

[delucchi-cmu]

Closes #460

Puts all the file reading on loading a catalog into a single module. This reduces the complexity for reading the code, reduces code duplication, and also reduces the number of times we need to read the properties file, and perform file system stat calls to determine if files exist. This should speed up catalog loading on remote file systems where there is a latency associated with each file read.

[codecov]

Codecov Report

Attention: Patch coverage is 98.21429% with 1 line in your changes missing coverage. Please review.

Project coverage is 92.63%. Comparing base (f2704b8) to head (d5478fc).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/hats/loaders/read_hats.py	98.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #394      +/-   ##
==========================================
- Coverage   92.83%   92.63%   -0.20%     
==========================================
  Files          49       49              
  Lines        2134     2091      -43     
==========================================
- Hits         1981     1937      -44     
- Misses        153      154       +1     

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[github-actions]

Before [f2704b8]	After [0b8a656]	Ratio	Benchmark (Parameter)
22.5±0.1ms	23.0±0.04ms	1.02	benchmarks.MetadataSuite.time_load_partition_info_order6
388±1ms	397±7ms	1.02	benchmarks.Suite.time_outer_pixel_alignment
93.5±1ms	94.7±0.6ms	1.01	benchmarks.MetadataSuite.time_load_partition_info_order7
126±0.5ms	127±0.4ms	1.01	benchmarks.time_test_alignment_even_sky
1.03±0.03ms	1.03±0.03ms	1.01	benchmarks.time_test_cone_filter_multiple_order
93.8±0.6ms	93.9±0.5ms	1	benchmarks.MetadataSuite.time_load_partition_join_info
110±0.9ms	109±1ms	0.99	benchmarks.Suite.time_paths_creation
46.5±0.5ms	46.3±0.6ms	0.99	benchmarks.Suite.time_pixel_tree_creation
15.1±0.8ms	13.9±0.9ms	0.92	benchmarks.Suite.time_inner_pixel_alignment

Click here to view all benchmarks.

[camposandro]

Thanks Melissa, the loading logic has become much clearer already! Left just a couple of comments about outdated docstrings.