Add 'erase_sectors' function to flash-algorithm

[9names]

With SPI flash, erasing sector-by-sector is much slowing than erasing by block.
The CMSIS flash algo standard doesn't provide an interface for doing a block erase.
By augmenting the flash_sector function with a "number of sectors to erase" parameter, we allow the flash algo to use larger erase blocks.

This change results in slightly more than a 2x improvement in erase times for large binaries.

Open questions:

• Should this take a start address and an end address instead, to help deal with regions with different sector sizes?
• Should the function be called something other than flash_sectors to make it less easy to confuse with flash_sector

This draft impl assumes that all sectors sent to the erase command are of the same size and are contiguous - before merging I need to write something to collect all contiguous areas into batches to pass on to erase.
This draft also includes an update to the rp2040 flash algo to exercise this functionality

[bugadani]

In the esp loaders we pretty much just ended up setting sector size to block size, and doing block erases in the flash algos, because I didn't want to add exactly this. However, if we're at it, I think I would prefer an erase(from, to) that would allow the flash algos to choose whichever is the best way to erase the required memory region.

[9names]

would you expect the to address to be inclusive or exclusive?

[bugadani]

I think exclusive is more logical, and easier to work with.

[bugadani]

How come you need that -1? If I'm not mixing up my intervals, the end of an exclusive range is just address + size 🤔

[9names]

My brain malfunctioning, basically 🤦.
I probably should have not done any programming today.