The RP2350 boot ROM seems to randomize memory on a HW reset, including
both CPU stacks where we normally stuff the "reset to bootloader" flag.
Update the docs and source to remove rp2040.enableDoubleResetBootloader()
on RP2350-based boards.
Fixes#2606
Call `rp2040.enableDoubleResetBootloader()` anywhere in the code to
enable the check. W/o that call, the checker will be linked in.
See #892
CORE1 doesn't start until well after the C runtime initialization,
so the flag won't be overwritten.
Also increase timeout to 350ms because OTA bootup can be
slow.