Add finger hole pull option to drawers

[Ttawannn]

Adds a handle_style option to the drawer front, so a drawer can use a finger hole instead of a protruding pull handle (or nothing at all).

The existing behaviour is unchanged: handle_style defaults to handle.

New options (Drawer section)

Option	Description
handle_style	handle (default), hole, or none
handle_hole_size	[width, height, depth]. Negative width/height is a fraction of the drawer front, matching the convention used by handle_size. A depth of 0 cuts through the front, a positive depth leaves a blind recess clamped to the wall thickness.
handle_hole_radius	Corner radius, -1 is height/2
handle_hole_open_top	Default true

handle_hole_open_top squares off the top of the hole and cuts it out through the top of the drawer front, leaving a notch with rounded bottom corners. There is no overhang, so it prints without supports. Set it to false for a fully enclosed hole, which then honours handle_vertical_center.

Implementation

• The hole is cut as another child of the existing drawer body difference(), and the handle is wrapped in if(handleStyle == "handle").
• New drawerFingerHole() module builds the rounded profile from a hull() of circles and extrudes it along the drawer front. A hull() is used rather than offset() on a square, because the square is degenerate when the radius is height/2.
• The new parameters are threaded through drawers(), drawer() and gridfinity_drawer().
• combined/gridfinity_drawers.scad regenerated with scripts/combined-openscad_script.ps1.

Testing

Rendered with OpenSCAD, all manifold with Status: NoError and no warnings: default handle, none, open top notch cut through, open top notch as a blind recess, enclosed hole, handle_hole_radius = 0, handle_vertical_center, the everything render, and the combined file.