Chip adapter

[DodoidOfficial]

This PR adds (KiCAD) hardware source files for the flash adapter, the PCB used to connect to an SPI flash chip while it is still installed on a board. It can be used to write-protect the chip, or to connect it to external programmers, logic analyzers, or other external devices. It will also be used together with the Flashkeeper FPGA board.

[DodoidOfficial]

Soldered adapter is in reasonably good shape I think, but I'm leaning towards replacing the edge fingers with a ZIF socket for a standard flat-flex cable so we don't need to deal with weird custom cables. The "hard to make" part passes DRC against JLCPCB flex PCB rules, checks out per their Capabilities page, and displays properly in their viewer now. Should work with other comparable fabs too.

I committed some documentation that may help people understand these files/this hardware.

I'd like to move forward with the solderless design soon (PCB in progress), but will need to get a (working) SLA printer before I can start prototyping them.

[tlaurion]

@DodoidOfficial ready for review with png updated and under docs/images and referred as desired under index.md and architecture docs?