gateware.iostream.{IOStreamer,IOClocker}: new components. `IOStreamer` is a reusable I/O buffer to stream adapter, suitable for interfaces where the clock is generated internally on the FPGA. `IOClocker` is a reusable I/O clock divider for use with `IOStreamer`.

protocol.nbd: implement Network Block Device server.

software: update `pdm.min.lock`.

applet.video.ws2812_output: modify to use port groups

applet.sensor.pmsx003: modify to use port groups

applet.interface.uart: modify to use port groups

gateware.uart: modify to use port groups

software: update `pdm.min.lock`.

firmware: bugfix: rejected control transfer lingers (-2 bytes XRAM). If a control transfer is rejected, in some cases `pending_setup` will remain true. Then the main loop will keep entering `handle_pending_usb_setup`, and there is a race condition with the `handle_usb_setup()` interrupt handler. Often the handle_usb_setup() interrupt handler will prevent follow-up correctly formed setup packets from completing. note: This bug was present before my code size optimization patches too.

firmware: add register keyword to optimize code size (+19 bytes XRAM). Note: this lowers code size by 18 bytes, and frees up 1 byte of statically allocated data