Is a safe 110/120VAC benchtop power tap possible?
Building one is unnecessary if you can just buy one. Particularly because making your own is a dangerous endeavour when it comes to mains-connected things. There are devices made for quickly connecting and disconnecting mains-voltage things in the safest manner possible; the Cliff Quicktest is one example. It's hard to get outside of Europe, but you may be able to find one. I understand there are some US distributors.

This type of device contains everything needed to relatively safely handle mains voltages, but keeps it as easy as possible to connect and disconnect. The connections are made by what are basically heavy-duty alligator clips, and knife switches integrated into the cover prevent any live metal being exposed when you open it up to connect wires. They also have fuses on at least the live wire, and some also on neutral, and some of the Cliff ones at least also have neon indicator lamps to show when it's live.

The colors of the clip levers are also generally made to match the building code standards for insulation colors, so it may be worth looking for one in your locale's colors. I think they come in UK, European, and US/Canada colors from Cliff, and you may be able to find ones in other colors from other manufacturers, if there are any others.

Note: I have no affiliation with Cliff Electronics. They are simply the only manufacturer I'm aware of for this type of device.