DS18B20 sensors require a strong pullup to be applied for the duration
of the temperature conversion, within 10us of the command. The rp2xxx
pins have sufficient drive strength to use as the pullup (no external
mosfet needed).

Add a new write_bytes_pullup() that will apply the pullup after
bytes are written. Existing read_bytes()/write_bytes() has no change to
onewire timing.

A pio_onewire_parasite example reads multiple sensors individually,
applying the strong pullup.