Pyproject and code organization

[drewoldag]

• Moving qp code and tests into ./src/qp and ./tests/qp respectively.
• Removing old files and directories that are no longer needed.
• Moving from setup.py to pyproject.toml.
• Updated various files as necessary to accommodate those changes.

[drewoldag]

I botched the creation of this PR, I'm closing it out, and creating a new PR against LSSTDESC/qp:main.