Grid stretching uses wrong array bounds for y_cc and z_cc

[sbryngelson]

Bug

In `src/pre_process/m_grid.f90`, the y-direction grid stretching uses `y_cc(0:m)` instead of `y_cc(0:n)`, and the z-direction uses `z_cc(0:m)` instead of `z_cc(0:p)`. This passes wrong array bounds to the stretching routine.

File: `src/pre_process/m_grid.f90`, lines 134 and 171

Impact: Grid stretching in y and z directions uses wrong cell counts, producing incorrect non-uniform grid spacing in multi-dimensional simulations with anisotropic resolution.

Severity: Critical — grid geometry is wrong whenever y/z stretching is used with different grid sizes per direction.

[sbryngelson]

Fix: #1181