only allow netcdf4 engine

this is a temporary restiction to ensure only correct
encoding for the output is used.

Related: pydata/xarray#7127

Author: observingClouds

xbitinfo/save_compressed.py

@@ -114,8 +114,10 @@ def __call__(
         for_cdo=False,
         time_dim="time",
         chunks=None,
+        engine="netcdf4",
         **kwargs,
     ):
+        assert engine == "netcdf4", "Only 'netcdf4' engine is currently supported."
         self._obj.to_netcdf(
             path,
             encoding=get_compress_encoding_nc(
@@ -127,6 +129,7 @@ def __call__(
                 time_dim=time_dim,
                 chunks=chunks,
             ),
+            engine=engine,
             **kwargs,
         )