Properly include generated Python files in the wheel

[llucax]

When building the wheel, the setuptools file discovery feature runs before the compile_betterproto sub-command is run, so the files are not included in the resulting wheel.

To overcome this issue we use a hack, by running the compile command early when the distribution options are being finalized, we make sure the files are present by the time the file discovery runs.

This is very hacky though, and even when it seems to work well in all tested cases (calling setuptools`setup() directly, build, pip install, pip install -e), I wouldn't be very surprised if it breaks in the future, so we probably will have to have an eye on it.

Unfortunately it seems there is no easy way to do this with setuptools:

• https://github.com/pypa/setuptools/discussions/3180#discussioncomment-2422328
• https://github.com/pypa/setuptools/issues/2591

This PR also includes some other improvements, including:

• Better abstraction of the configuration object
• Better hooking into setuptools
• Use of logging instead of print
• Better name for the command to compile the proto files

[Marenz]

Approved, but removed from the queue in case you want to react to the feedback

[llucax]

Updated:

• Improved the warnings to add more hints on the impact and how to fix them and added a missing warning
• Calculated the dest_dir only once
• Renamed copy_with_path to copy_with_directories and improved the docs
• Fixed the misplaced return in the commits

[llucax]

Re-enabling auto-merge.