Port all environments from box2d to pymunk

The Python bindings for box2d, even with the newer dependency switched to, haven't been maintained in ~6 years, whereas the python bindings for pymunk are actively maintained, better documented, and the maintainer of pymunk a few years back indicated that he intended to keep maintaining pymunk roughly for life. This will require environment version bumps.

I assume for legacy reasons we should still leave them named box2d, but I'm moderately uncertain about that

Edit: The most useful environment for us to port over first is bipedal walker, because it's additionally used by PettingZoo, MO-Gymnasium and MOMAland

Edit 2: The box2d python bindings don't have python 3.14 support, making this especially urgent

Edit 3: The way we want to handle this is to put all the environments into a new "pymunk" environment class, keeping the version numbers of the environments and bumping one, do a release or two with box the box2d and pymunk environments with warnings in each class to report bugs in the new pymunk environments and that the box2d environments are going away, and then eventually yank the box2d class