Big merge to kick-off 4.0 development: Upgrade to Pyglet 3, Pymunk 7, and a new WebGL backend

[Cleptomania]

Basically does what it says on the title, this merge will mark the start of 4.0 development in the development branch of Arcade.

What's done as of this merge from the pyglet-3 branch is:

• Basic compatibility/upgrade to Pyglet 3.0.dev1 release
• Upgrade to pymunk 7
• A new WebGL backend for arcade.gl which works alongside Pyglet 3's new pyodide backend to run in web browsers. Additionally there is a new webplayground folder for early testing of this. This is not quite ready for end-users as of this merge, but is close and people who aren't afraid of some rough edges could start to play with it
• The future.input module has been graduated to the top level, may still get more tweaking as part of 4.0
• Re-works CI pipeline to run tests in Github Actions hosted runners with xvfb and Mesa's software renderer instead of our dying laptop in the basement. All CI jobs have also been converted to use uv for better caching and improved performance, they all run much faster now.