Bambu Lab Reusable Spool - Optimized

Remix of the original Bambu Lab reusable spool. Reduced the material used for the side walls to a minimum while keeping overall strength and rigidity resulting in ~20-25% less print time and material usage. With the open design you can see how much material is left on the spool. Also added some holes on the inner cylinder so you can fix the filament for spooling.