add support for Metro rp2350 USB SNES-like controller

[FoamyGuy]

Also:

• removed USB HID device handling code that was unused by this project.
• changed to use a single core & setup/loop functions
• added prints during setup to output which pins are in use for USB

[TheKitty]

Some comments still refer to two cores
For rp2040 pico-pio-usb, calling USBHost.begin() on core1 will have most of the
// host bit-banging processing works done in core1 to free up core0 for other works

[FoamyGuy]

Thank you, the reference to different cores are removed with the latest commit.