convert setup.py and related files to pyproject

[Jerakin]

Modernize the build files.

Some notes of interest.

• Both the manifest and setup.py included ["*.png", "*.qss"] but there are no files matching it - I removed these.
• The .svg file within the ui folder was never included - I added this to be included.

Which is the minimum version supported?

• The manifest indicates minimum version is 4.2 but resent activity seems to indicate that 4.0 is supported.
• blender_manifest.toml wasn't introduced until 4.2.
• Furthermore the README.md says minimum version is 2.83. Do note that 2.83 will not work with bqt due to the encoding argument for logging.basicConfig wasn't added until 3.9 (which would make the minimum version Blender 2.93)

Note: The build-system version might have to be changed depending on which blender version is targeted. Last version of setuptools with support for 3.8 is 60.2.0

[hannesdelbeke]

The reason for version mismatch is

blender moved from addons to blender extensions.
so i made bqt compatible with extensions, and upgraded from 1.x.x to 2.x.x to make it clear this is a breaking change.
this way people can choose between the bqt addon or the bqt extension.
if you think this is not the right approach, we can change versioning, since there hasn't been a 2.x.x release on pypi yet.

note that, since 1.4.2 is already released, we can not match this.
and ideally i only update 1 version, since i need to do so every time i make a release.
i would consider dropping the old addon setup since this is now considered legacy.

[hannesdelbeke]

i also like that we moved to toml, which i use for all my own projects. i'll have to test if it works with the bqt release process, it looks good on glance.

[hannesdelbeke]

since pyside6 is now a dependency, we can use the minimum version for python that pyside6 supports
currently that's Python <3.15, >=3.9
so below 3.9 is excluded

https://vfxplatform.com/ suggests python 3.11 or higher, and pyside 6, but i know blender an get funny about staying in line with the vfx platform.

[Jerakin]

i would consider dropping the old addon setup since this is now considered legacy.

Support for old addon setup can only be dropped if the minimum version of the bqt is 4.2. I mentioned in #133 that I do think that should be the minimum version (Earliest LTS version still receiving support).

since pyside6 is now a dependency

I will add a note on this in this PR #136

https://vfxplatform.com/ suggests python 3.11 or higher

vfxplatform is very useful however for our case here the python version we support should be indicated by the Blender version (which with Blender 4.2 would coincidentally be 3.11).

[Jerakin]

Let me know which version of Blender you think we should be the lowest supported and I will update this PR

[hannesdelbeke]

blender 4.2 sounds good
while we're at it. let's also do 3.11 for python, since it matches anyway.

[Jerakin]

What's left on this is

• i'll have to test if it works with the bqt release process

If that works then this is good to merge.

P.s. I will make a separate PR making 4.2 the minimum supported version.

[hannesdelbeke]

i'll just accept this PR and try release a package.