Changes build system to flit

[AlejandroFernandezLuces]

Overview

To standarize the project, I moved the build system to flit, which uses the pyproject.toml standard. This file allows the project building to be tool independent.

[RobPasMue]

cache-dependency-path: requirements_test.txt has to be adapted to use pyproject.toml in the workflow ;)

[codecov-commenter]

Codecov Report

Merging #7 (b245bc1) into main (eafb8fb) will increase coverage by 0.22%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main       #7      +/-   ##
==========================================
+ Coverage   83.56%   83.78%   +0.22%     
==========================================
  Files           1        2       +1     
  Lines          73       74       +1     
==========================================
+ Hits           61       62       +1     
  Misses         12       12              

Impacted Files	Coverage Δ
pytest_pyvista/pytest_pyvista.py	83.56% <ø> (ø)
pytest_pyvista/__init__.py	100.00% <100.00%> (ø)

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[AlejandroFernandezLuces]

I'm not sure how to handle the cache option in actions/setup-python@v4, since now we are managing all of the project dependencies with flit. Currently, I removed it because I don't know if there is any way to keep a cache of the packages with flit.

Is there any option to cache the installed packages using flit @RobPasMue ?

[RobPasMue]

I think that's the only thing you need @AlejandroFernandezLuces :)

[RobPasMue]

The way cache-dependency-path works is by checking the checksum of whatever file you provide. If it doesn't change, it will use the stored cache with that hash/checksum. Otherwise, it'll generate a new one. Just keep that in mind.

I also saw that you were installing it using flit directly. I recommend that you keep using pip for doing the install process. That way you can make use of the cache: 'pip' option. I left you another suggestion.

[MaxJPRey]

Thanks @RobPasMue for looking at the PR. Much appreciated.

[MaxJPRey]

This comment might be useful for future maintenance. Thanks for adding it.

[MaxJPRey]

LGTM.