Dev/model generation speedup

Adapts the code to speed up model generation from 11ms/model (initial) to 6-7ms/model by:

• Introducing shortcuts for euler angles for unity and 180° x-Axis rotation (1ms / urdf)
• Storing the module graph instead of re-computing the property (2ms / urdf)
• Remove redundant call to assembly graph (.4ms / urdf)
• Rounding transformations to 12 decimal places (1ms / urdf), I suppose mostly because x e-16 becomes 0.
• Reducing complexity in matrix multiplications (marginal gains)

all numbers based on Schunk modules