bed_mesh: reduce split_z_delta minval

This allows for visible improvements in surface quality.

Author: tg73

klippy/extras/bed_mesh.py

@@ -1294,7 +1294,7 @@ def _apply_offsets(self, point, offsets):
 class MoveSplitter:
     def __init__(self, config, gcode):
         self.split_delta_z = config.getfloat(
-            'split_delta_z', .025, minval=0.01)
+            'split_delta_z', .025, minval=0.001)
         self.move_check_distance = config.getfloat(
             'move_check_distance', 5., minval=3.)
         self.z_mesh = None