Add pytest to sanity check basic example

[joshkamm]

• create new branch
• add pytest task, feature, and dependency in pixi.toml
• use task dependency to run test so pytest can assume the output already exists and just read it
• add pytest to pixi start task
• use the test function to check that the output integrals are similar to a pre-saved sample output
• try relative tolerance 10^-6 and absolute 10^-6
• move python test file
• add pycache to .gitignore
• ask which matrices I should test - Paul said A, S, En, T, pVp, and Ciap are all good
• figure out how to test multiple matrices in single file for SENT
• create pr