Use ByteFifo in tunnel USART, add loopback

MainBoard: Invalidate parts.xlsx

MainBoard: Add filter capacitors to buttons

MainBoard: Change power circuit to make ON button connected to GND

MainBoardBRD: update DRC and reroute DRV8833 driver power supply - update DRC and save it as `robotikabrno-4-layers.dru` - optimize values according manufactors 4 layers stack capabilities

Fix fifo overrun

Add ByteFifo prototype

MainBoard: 4 layers, motors connector, DRV8833, libraries - set 4 layers stack + change DRC setting about same signals, the rest is still same (possible place for improvements due to 4 layers stack and https://jlcpcb.com/capabilities/Capabilities) - motors connectors - remove terminal blocks, replace pinheads with JST-PH6 (2mm x 6 pins) - DRV8833 - improve `DRV8833.lbr` library - fix thermal GND pad under the package - reroute on DPS and add thermal VIAs according http://www.ti.com/lit/an/slma004b/slma004b.pdf - reroute `Q1` and `Q2` + main power terminal block - libraries - add `jst-ph.lbr` and document `LIBRARIES.md` with source info about used libraries - please extend the `LIBRARIES.md` in the feature

Add USART1 receive logic

Add DMA-enabled transmission for USART1