[MatLib/MPL] Drop Independent Variables Parent Tag

Time loop refactorings

The function can decide this on its own now.

This is similar to the staggered scheme implementation.

Avoid use of independent process_id variable in the loop,
reuse the process_data.process_id.

Split into isMonolithicProcess(pcs_data) query and
the staggered scheme coupled solutions preparations.

BHE 2U implementation

remove white space

relax the tolerance a bit