Losslessly compress PNGs

[hugovk]

Use https://github.com/shssoichiro/oxipng to reduce by about 15%.

They're not too big to begin with, but might as well save a bit more?

❯ oxipng -o max --strip all --recursive .
Processing: ./src/pymanager/_resources/setupx44.png
Processing: ./src/pymanager/_resources/pythonwx150.png
Processing: ./src/pymanager/_resources/pythonwx44.png
Processing: ./src/pymanager/_resources/pyx256.png
Processing: ./src/pymanager/_resources/setupx150.png
Processing: ./src/pymanager/_resources/pythonx50.png
Processing: ./src/pymanager/_resources/pythonx150.png
Processing: ./src/pymanager/_resources/pythonx44.png
1512 bytes (15.48% smaller): ./src/pymanager/_resources/pythonx44.png
3209 bytes (15.06% smaller): ./src/pymanager/_resources/setupx44.png
1541 bytes (16.43% smaller): ./src/pymanager/_resources/pythonwx44.png
1813 bytes (15.83% smaller): ./src/pymanager/_resources/pythonx50.png
4609 bytes (9.36% smaller): ./src/pymanager/_resources/pythonwx150.png
11882 bytes (18.74% smaller): ./src/pymanager/_resources/setupx150.png
4714 bytes (9.90% smaller): ./src/pymanager/_resources/pythonx150.png
7735 bytes (9.36% smaller): ./src/pymanager/_resources/pyx256.png

[zooba]

Hopefully it doesn't mess with the rendering - these get shown in places in the OS that aren't a browser, so potentially more fussy. But we'll have beta releases to check it out, and can always roll back.