This introduces an additional marker to the state partition right after the magic which indicates whether the current progress is valid or not. Validation in tests that we never write without an erase is added.
There is currently a FIXME in the FirmwareUpdater. Let me know if we should take the erase value as a parameter. I opened a feature request in embedded-storage to get this value in the trait. Before this, the assumption about ERASE_VALUE=0xFF was the same.
FirmwareWriter currently has a "max-write-size" parameter, but this is a limitation that should be handled by chunking inside the NorFlash driver, and not "up here" in user code. In case that the driver (e.g. qspi driver) is unaware of any max-write limitations, one could simply add an intermediate NorFlash adapter providing the chunk'ing capability.
