Migrate over dodiscover CI/CD tests

[adam2392]

Systematically migrate independence test, documentation and unit tests one at a time.

[adam2392]

Suite of tests we should migrate over from dodiscover are:

• Chi-square
• G^2 (note there might be discrepancies between G^2 implementation vs Chi-square general approach)
• FisherZ (i.e. partial correlation)
• KernelCI
• ClassifierCI
• RegressionCI
• ClassifierCMICI
• CMICI
• Oracle
• KernelCD
• Bregman

Along the way, Monte Carlo and kernel utility functions should be ported.

Simulation functions that help test the code should also be added here since those don't require the input of a graph:

• nonlinear_additive_gaussian

Also the test data should be moved here:

• testdata.py for G^2 implementation
• adult.csv for Chi-square

From dowhy: @bloebp can start moving over tests too and consolidating with the above list where applicable.

Once done, we can also compare implementations vs causal-learn and then migrate any improvements that are there but not in the above implementations (if any), and then fully remove CI/CD tests in general and create dependencies on pywhy-stats.