Introduce basic pyproject.toml, supporting existing build methods only #176

Job	Run time
Build wxPython documentation	0s
build-source-dist	8m 38s
build-wheels (ubuntu-22.04, 3.9, x64)	24m 2s
build-wheels (ubuntu-22.04, 3.13, x64)	23m 19s
build-wheels (windows-2022, 3.9, x86)	25m 16s
build-wheels (windows-2022, 3.9, x64)	22m 48s
build-wheels (windows-2022, 3.13, x86)	23m 5s
build-wheels (windows-2022, 3.13, x64)	21m 39s
build-wheels (macos-13, 3.9, x64)	30m 57s
build-wheels (macos-13, 3.13, x64)	33m 46s
Publish Python distribution to PyPI	0s
Upload wheels to snapshot-builds on wxpython.org	0s
Create GitHub Release and upload source	0s
	3h 33m 30s

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