[Feature]: parse collision information in the MJCF

[TheotimeLH]

🚀 Feature

It seems the collision pairs are not retrieved from MJCF xml files,
So loading from a MJCF results in an empty geom_model.collisionPairs.

Motivation

In the MJCF xml files, collisions are described using contype and conaffinity bit mask matching. The current alternative, which is to add all possible collision pairs by hand, does not leverage this.

Alternatives

Until now, it seems people add the collision pairs by hand

Additional context

No response

Checklist

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