UART write never blocks and doesn't actually write to GPIO pins

[c1570]

Writing to the UART never blocks at the moment:

rp2040js/src/peripherals/uart.ts

Line 76 in 61e1d2c

return (this.rxFIFO.full ? RXFF : 0) | (this.rxFIFO.empty ? RXFE : 0) | TXFE;

This also means that printf() using pico_stdio_uart is way faster in emulation than in reality quite often (basically whenever the silicon 8 byte TX buffer is exhausted).

Additionally, using the UART doesn't actually change the GPIO pins but only triggers the onByte() callback:

rp2040js/src/peripherals/uart.ts

Line 119 in 61e1d2c

this.onByte?.(value & 0xff);

Probably not a big deal but worth documenting anyways.