Obtain the correct number of particles in catalog

[camposandro]

Compute the correct number of particles in a catalog. Closes #9.

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Code Quality

• [X] I have read the Contribution Guide
• [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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[github-actions[bot]]

Before [59d83c67]	After [a618b7bc]	Ratio	Benchmark (Parameter)
1.46±0.5s	3.35±1s	~2.29	benchmarks.time_computation
1.18k	2.7k	2.30	benchmarks.mem_list

Click here to view all benchmarks.

[codecov[bot]]

Codecov Report

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

Files	Coverage Δ
src/corrgi/corrgi.py	93.75% <100.00%> (+0.41%)	:arrow_up:
src/corrgi/utils.py	91.66% <100.00%> (+2.77%)	:arrow_up: