TL: generic FieldsIO class for n-dimensional rectilinear grids + VTK support (#533)

* TL: simplified fieldsIO to two generic classes (Scalar + Rectilinear)

* TL: trying something

* TL: restriction to python 3.11

* TL: another try

* TL: I'm dumb

* TL: yet another try ...

* TL: added vtk support for 3D VTR files

* TL: avoided clashing name, gitignore update

* TL: you gotta be kiding me ...

* TL: VTK output support for Rectilinear FieldsIO

* TL: added documentation

* TL: polished documentation

* TL: minor typo

* TL: refactoring following thomas's suggestions

* TL: minor typo

* TL: corrected Rectilinear.toVTR for paraview groups