[Python] Add (and use) a robot_loader function

[nim65s]

To avoid code duplication and ease future robot addition.

While here:

• sync submodule
• use import pinocchio as pin
• deprecate loadTalosLegs() for the factorized loadTalos(legs=True) (and update tests accordingly)
• deprecate loadTalosArm() for the factorized loadTalos(arm=True) (and update tests accordingly)
• deprecate loadTalosNoHand() for the factorized loadTiago(hand=False) (and update tests accordingly)
• use cleaner os.path.join() for file path manipulation instead of string concatenation
• infer most subpaths ("path / robots" in most cases & "path + srdf" in all cases)

https://gitlab.laas.fr/gsaurel/example-robot-data/pipelines/10241 (one job is failing because of an on-going CI upgrade)

[nim65s]

This is a first step of small internal refactors to ease maintenance and new robot additions.