Extended retalicon spring rest

This serves the same purpose as DartKraft's [original Retalicon spring rest](https://www.thingiverse.com/thing:2431557), except that the part that interfaces with the back of the recon shell is larger and thicker, which should make it stronger, and the back of the spring is held at the appropriate position for a stock spring with no need for spacing rings.

This may need to be printed either with supports, or upside-down, to prevent the surface that meets the back of the recon shell from suffering from the droopy lines of plastic that can occur while bridging.