Enable AVX-enabled builds

[traversaro]

Comment:

MuJoCo PyPI builds use AVX, and so it may be confusing for users not to get have these optimization in the conda package. Thanks to conda-forge/conda-forge.github.io#2091, we should be able to have AVX-enabled packages for MuJoCo.

[traversaro]

Once #41, we can easily use the mujoco-testspeed to roughly compare the different package variants performances.

[traversaro]

Just to give an idea why this is worth, my quick&dirty benchmark is the following, run testspeed (mujoco-testspeed in conda packages) with the model https://github.com/google-deepmind/mujoco/blob/3.1.3/model/humanoid/humanoid.xml , i.e. mujoco-testspeed ./humanoid.xml 100000 . The current results are (this is simulation time, so less is better):

• ~1.81 for the upstream build
• ~2.45 for the conda-forge build