Magnetic tool holder - parametric!

I really liked DaVinci2000's magnetic tool holder, but wanted a longer length to hold all of the tools for my Ender 3. I decided to make a parametric version of the design, so that anyone can just specify the desired total length in the parameters in Fusion, and the design will automatically update, including the proper number of magnet holes. This is also useful in the case that someone needs to use larger diameter magnets than the original - all they should have to do is edit the magnet width parameter. The current length is 101.6mm, which is 4 inches.