Eliminate redundant dimension parameter for BConds

[matt-frey]

In GitLab by @vinciguerra_a on May 26, 2023, 15:47

The changes in !173 reduce repetition of template parameters across IPPL, but these changes have a risk of introducing a dependency loop between ippl::Field and ippl::BConds. Fields have an instance of their boundary conditions, so Field depends on BConds. The only information BConds needs from the field a priori is the rank. This can be extracted via Field::dim, but then BConds would depend on Field at compile-time, introducing a dependency loop.

In !173, this is resolved by passing an additional template parameter to indicate the dimension. This parameter is semantically redundant, but breaks the loop. Ideally, this should be resolved with no redundant information, as this was the original intent of the MR.