The encoding/binary package in Go 1.23 imports the slices package, which
results in circular import when imported from the machine package.
Therefore, encoding/binary cannot be used in the machine package.
This commit fixes that by introducing a new internal/binary package that
is just plain Go code without dependencies. It can be safely used
anywhere (including the runtime if needed).
machine/stm32, nrf: implement machine.Flash
Implements the machine.Flash interface using the same definition as the tinyfs BlockDevice.
This implementation covers the stm32f4, stm32l4, stm32wlx, nrf51, nrf52, and nrf528xx processors.