Remove redundant pixel tree builder class

[camposandro]

Removes the redundant pixel tree builder class as it is no longer needed - the pixel trees can be instantiated using PixelTree.from_healpix. Closes #253.

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Code Quality

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• [X] My code follows the code style of this project
• [X] My code builds (or compiles) cleanly without any errors or warnings
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[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 94.19%. Comparing base (67b4f8e) to head (70b90d3).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #266 +/- ## ========================================== - Coverage 94.22% 94.19% -0.04% ========================================== Files 56 55 -1 Lines 1940 1928 -12 ========================================== - Hits 1828 1816 -12 Misses 112 112 ```

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Before [67b4f8ec]	After [32d3462d]	Ratio	Benchmark (Parameter)
77.4±0.2ms	78.8±1ms	1.02	benchmarks.MetadataSuite.time_load_partition_join_info
41.2±1ms	42.1±0.5ms	1.02	benchmarks.Suite.time_pixel_tree_creation
122±1ms	124±0.8ms	1.02	benchmarks.time_test_alignment_even_sky
13.8±0.2ms	14.1±0.1ms	1.02	benchmarks.time_test_cone_filter_multiple_order
77.6±0.2ms	78.6±2ms	1.01	benchmarks.MetadataSuite.time_load_partition_info_order7
20.2±0.4ms	20.1±0.5ms	1	benchmarks.MetadataSuite.time_load_partition_info_order6
13.2±0.2ms	13.2±0.2ms	1	benchmarks.Suite.time_inner_pixel_alignment
82.9±2ms	82.9±2ms	1	benchmarks.Suite.time_paths_creation
368±4ms	362±2ms	0.98	benchmarks.Suite.time_outer_pixel_alignment

Click here to view all benchmarks.