feat(PP): RDI support and refact BinMappingPP

This commit deeply refactor the BinMappingPP.

Improvements are:

1. Support binMapping for RDI in beam coordinates.

2. Performance improvements:
   a. The previous code,LeanInterp, although faster than
      interp1 was not portable or flexible enough for all cases.

   b. We now interpolate at the same time all beam1[2,3,4]
      variables by using constrained 2d interpolation with
      `GriddedInterpolant`.

   c. Several clean-ups in logic, such as for handling the above,
      variable creation, tests and overall flexibility.

3. Regression tests provided.