chore: switch mojo dependency to PyPI mojo-mujoco-wrapper

[aditya-neuraco]

Switches the mojo dependency from a Git URL to the PyPI package mojo-mujoco-wrapper.

• mojo @ git+https://github.com/stepjam/mojo.git@0.1.1 becomes mojo-mujoco-wrapper>=0.1.1.
• The import name is unchanged (import mojo); mojo-mujoco-wrapper is the PyPI distribution name for the same library (the name mojo was already taken on PyPI).
• Its own dependencies (mujoco, dm_control, numpy) stay compatible with the versions bigym already pins, so nothing else changes.

This is a step toward publishing bigym to PyPI, which does not allow Git-URL dependencies.

Related PRs

• fix: remove trailing comma from pytest parametrize argnames #50 (remove trailing commas from pytest parametrize argnames) — should merge before all of these PyPI-prep PRs; it unblocks test collection on modern pytest (9.x).

[stepjam]

LGTM