Update target_selection build, linting, and formatting

[albireox]

This is a major engineering change of the build system, linting, and formatting, but otherwise it doesn't change anything in the code itself or how it works.

• The build system has been updated to using poetry as the PEP517 backend. The setup.py and setup.cfg files have been removed.
• Now we are using ruff for formatting and linting. The configuration is mostly the default ruff one but keeping the line length of 99 characters. All files have been reformatted.
• Added workflows to lint, check the lockfile, release, and test that the package imports.
• Updated the Sphinx and RTD configurations.