The netcdf cache function validates the cache by comparing the ds argument and other function arguments to the pickled arguments. If they match, the cache can be used.

Currently, just the coordinates of the argument ds and the output ds had to match, introducing two errors:
- If the data_vars differ and are used the cache is falsely valid
- The coordintates of the ds argument has to match the coordinates of the output ds. This limits the use of the cache function.

The PR compares the hash of the coords and data_vars of the ds argument to those that were stored in the pickle together with the cached output ds.

Ideally, the cache.cache_netcdf() accepts arguments that specify specifically which data_vars and coords need to be included in the validation check. Beyond the scope of this pr.