add box pieces for a vent kind of look

no particular reference for this, just took some "slashes" and cut them
out of the walls with the expectation of using the inner wall in a
different color. designed, as much as I'd call it a design, for the Eva
stick, but this is mostly just me trying stuff at the moment

Signed-off-by: Brian S. Stephan <bss@incorporeal.org>

src/frames/pieces/box/side-windowed-forwardslashes.scad

@@ -0,0 +1,22 @@
+/*
+ * SPDX-FileCopyrightText: © 2024 Brian S. Stephan <bss@incorporeal.org>
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ */
+
+include <parameters.scad>
+include <components.scad>
+use <side.scad>
+use <side-inner-wall.scad>
+use <side-windowed-backslashes.scad>
+
+module forwardslashes_windowed_side_box_frame_piece() {
+	difference() {
+		side_box_frame_piece();
+		// subtract slashes from the frame wall
+		mirror([0, 0, 1]) backslashes();
+		// subtract the inner wall area that will be provided by the other piece
+		side_inner_wall_frame_piece();
+	}
+}
+
+forwardslashes_windowed_side_box_frame_piece();