Application of Filters is not idempotent

[benjaminleighton]

I'm fairly sure that applying a time filter on a elev2D but probably all data objects changes the held xarray Dataset object making reuse of that SCHISMDataBoundary for a different time not possible. I think this problem is prevalent across everything using Filter and DataGrid or DataBlob

[benjaminleighton]

bug_filtering.zip

This appears to be due to non-idempotent behavious in filter and we've narrowed it down to self.filter.crop.update({self.coords.t: Slice(start=start, stop=end)}) in ocean_forcing.elev2D._filter_time. See attached notebook