Change `Field.__repr__` to match representation in `pystencils.fields`

repr of Field should look like

y: uint16_t[246,704,558]
x(3): float[20,40]

to match representation when using pystencils.fields

E.g.

In [3]: pystencils.fields('x: float32[20,40]')                                                                                                                                                                                                                                
Out[3]: x: float[20,40])

In [4]: pystencils.fields('x(3): float32[20,40]')                                                                                                                                                                                                                             
Out[4]: x(3): float[20,40])

pystencils/field.py

@@ -392,7 +392,12 @@ class Field(AbstractField):
         return self.dtype.numpy_dtype.itemsize
 
     def __repr__(self):
-        return self._field_name
+        if self.index_shape:
+            return f'{self._field_name}({",".join(str(i) for i in self.index_shape)}): ' \
+                f'{str(self.dtype)}[{",".join(str(i) for i in self.spatial_shape)}])'
+        else:
+            return f'{self._field_name}: ' \
+                f'{str(self.dtype)}[{",".join(str(i) for i in self.spatial_shape)}])'
 
     def neighbor(self, coord_id, offset):
         offset_list = [0] * self.spatial_dimensions