mo_grid_io add cache_size and static_contiguous options to output dataset

This merge request adds optional NetCDF cache/chunk control to mo_grid_io output datasets.

It introduces cache_size (MB) and static_contiguous as optional arguments to output_init. When cache_size is set, output variables derive spatially motivated chunk sizes from the cache budget and pass the resulting chunksizes, cache_size, and cache_preemption=100 to NetCDF. Static variables can optionally be written as contiguous storage via static_contiguous=.true.. If cache_size is not provided, the previous behavior is kept unchanged.