SillyShell Niper for Yeethammer

I found there was a slight bit of wobble using the Collet Nut and O-Ring version, leading to reduced consistency of shots, but wanted more securing and adjustment points for the screw-based version. This lets you secure at top and bottom and across four sides, allowing precise adjustment to get the barrel aligned straight and without any wobble. Also added the non-eject mechanism from Astropulse for use in Yeethammer. Designed to use heatset inserts but I only ended up using them for the top layer, I don't think it really needs them.