Box Cutter with Smooth Operation

This is a remix of the excellent design #5327492

There were three aspects I wanted to improve:
1. I thought that the actuation distance was more than necessary and risked plastic deformation of the lever arm over time.
2. When sliding the "handle" out or in, the catch would very often snag on burrs on the blade, requiring the user to wiggle the blade directly to free it up.
3. When sliding the "handle" back in to the seated position, the blade rotates very slightly, which causes the point near the keyring to cut in to the groove. Again the only way to free it up is to pull on and wiggle the blade directly.

To solve #1, I lowered the top surface of the catch by a bit over 0.5mm.
To solve #2, I rounded the top surface of the catch and the bottom surface of the pin holding the blade so that the two surfaces would engage and slide over one another instead of catching on the burr of the blade. To allow clearance for the pin, I created a slightly recessed channel in the slid