freq_offset not saved in netcdf variable metadata

[mdunphy]

When using freq_offset to output snapshots between output intervals (eg, saving on the half-hour at hourly intervals), the value of freq_offset is not saved as a netcdf variable attribute. Meanwhile the time_instant and time_counter variables contain output times without freq_offset applied, so they do not correspond to the actual output times of the snapshots. Without this freq_offset metadata, there is no way to reconstruct the output time vector.

Proposed workaround/solution: attached is a patch that adds freq_offset to the netcdf variable attributes, such that one can add it to time_instant to get the correct output time vector

[mdunphy]

Patch to add freq_offset to netcdf variable attributes