junction box faceplate compatibility

Looking at some of the 3D printed keystone plates that @JaredC01 designed I realized something: what if you just made an adapter plate that could use existing wall faceplates, in order to leverage all the existing off the shelf stuff out there?

The North American standard for this is [NEMA WD-6](https://www.nema.org/standards/view/wiring-devices-dimensional-specifications) (account required to download a free watermarked copy of the standard). Here are the important parts:

- Hole spacing for box/keystone plates: 3.281" +/1 0.01
- Hole spacing for yoke mount (like switchplate): 2.375" +/- 0.01
- Hole spacing per device(multi-gang): 1.812" +/- 0.01
- The box (and device) holes are tapped for a `#6-32` UNC screw
- Wiring device max envelope (aka box inside): 1.750" x 2.812"
- Single-gang faceplate standard min dimensions: 2.740" x 4.490"
- Each additional gang increases the min width by 1.812"
- Single-gang faceplate standard max dimensions: undefined

So:

- 2U is 3.504", screw holes could fit vertically (with faceplate overlap of 0.4"+ above/below) and @JaredC01's existing designs look _suspiciously_ close to 3.281" (although he's using 4 screws per plate and M3x6mm screws). It could also hold up to 3 single-gang or two 2-gang(with some plate overlap) across
- 1U is 1.752" and single-gang box is 1.750" horizontally, so it would _just_ fit but there would be 0.5"+ faceplace overlap above and below.
- 3U is 5.256" and could fit a 2-gang faceplace(4.552") horizontally with no overlap above/below.
- The 10" rack usable width of 8.75" is enough for a 3-gang faceplace vertically(8.176") with no side overlap, and you could fit two faceplaces horizontally but with a tiny bit protruding on the side (might not block the rack screws)
- In general it might waste a little bit of space as those plates are designed to cover the seam between the box and wall. Custom plates can usually be more space efficient.

These are all using the *MINIMUM* faceplate dimesions of 2.740" x 4.490". Many plates are larger: in my house I found the "premium" Leviton faceplates are 3"x5". (But the Monoprice keystone plates _are_ the min 2.75" x 4.5")

Does it make sense to do this? If so, what designs? Possibilities:

- 2U tall, vertical, one 1/2/3-gang, two 1/2-gang
- 1U tall, horizontal, one/two single-gang
- 3U tall, horizontal, one/two 2-gang

No repository file or test is named. Start by reviewing the existing 3D-printed keystone plate designs referenced in the issue and compare their dimensions with the listed NEMA WD-6 spacing, screw, and faceplate constraints; done means an agreed set of adapter designs and supported faceplate configurations.

Written by the indexing model from the issue text.