refactor: update exception message

[tlambert03]

yet another update to how the emit loop error exception looks. with this PR it will now look something like this:

While emitting signal 'ndv.models._mapping.ValidatedEventedDict.value_changed', an error occurred in a callback:

  ValueError: Dimensions {0, 1, 2} do not exist. Expected one or more of ('time', 'lat', 'lon')
  ---------------------------------------------------------------------------------------------

  SIGNAL EMISSION: 
    /Users/talley/dev/self/ndv/src/ndv/controllers/_array_viewer.py:302 in _on_view_current_index_changed
      self._data_model.display.current_index.update(self._view.current_index())
    /Users/talley/dev/self/ndv/src/ndv/models/_mapping.py:187 in update
      self.value_changed.emit()  # <-- SIGNAL WAS EMITTED HERE

  CALLBACK CHAIN:
    /Users/talley/dev/self/ndv/src/ndv/controllers/_array_viewer.py:275 in _on_model_current_index_changed
    ... 6 more frames ...
    /Users/talley/dev/self/ndv/.venv/lib/python3.12/site-packages/xarray/core/utils.py:802 in drop_dims_from_indexers
      raise ValueError(  # <-- ERROR OCCURRED HERE 

      Local variables:
            indexers = {1: slice(None, None, None), 2: slice(None, None, None), 0: ...
                dims = ('time', 'lat', 'lon')
        missing_dims = 'raise'
             invalid = {0, 1, 2}

[codspeed-hq]

CodSpeed Performance Report

Merging #351 will not alter performance

_{Comparing tlambert03:update-err-message (01270c8) with main (2179994)}

Summary

✅ 67 untouched benchmarks

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (2179994) to head (01270c8).
Report is 7 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##              main      #351   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           21        21           
  Lines         2095      2115   +20     
=========================================
+ Hits          2095      2115   +20     

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