Add benchmarks for projected correlation

[camposandro]

Implements benchmark suite for the projected correlation.

• [ ] My PR includes a link to the issue that I am addressing

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
• [X] My code contains relevant comments and necessary documentation

[codecov[bot]]

Codecov Report

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

[github-actions[bot]]

Before [b18cc976]	After [e611c056]	Ratio	Benchmark (Parameter)
1.17±0m	1.18±0m	1	benchmarks.ProjectedSuite.time_pccf_davis_peebles_estimator
3.64±0m	3.64±0m	1	benchmarks.ProjectedSuite.time_pcf_natural_estimator

Click here to view all benchmarks.