Use pyproject.toml for project metadata and build-system

[mwtoews]

This PR modernises this project to use pyproject.toml as supported by setuptools to handle project metadata (PEP 621) and define the build-system.

Modern tools like uv can benefit from this PR.

Other changes:

• Remove and ignore gempy/_version.py
• Remove setup.py and setup.cfg files, which are no longer needed in modern projects
• Update the Source Code URL
• Remove author_email, as it does not have a 1:1 author:email; if one or more emails want to be assigned to the table, this can be done easily (in this PR or subsequent)
• The -r requirements.txt syntax is not supported by setuptools' dynamic functions, so is commented out -- I suggest migrating from these files to embedding requirements into pyproject.toml
• Change setuptools.packages.find from the "exclude" strategy to the "include" strategy, to prevent accidentally including other directories.

[mwtoews]

I'm not sure how to "Log in to TeamCity" since "TeamCity build failed".