Transport-agnostic (xfer callback) layer with a JEDEC-ID chip database
and detect/read/erase_sector/program_page/program/verify. Standard
opcode set, 3- and 4-byte addressing (4-byte command opcodes for parts
over 16 MB). Seeded with the KCU105's MT25QU256 plus common
Winbond/Macronix/ISSI/Micron parts.
detect + read validated on the KCU105 over the proxy. erase/program are
implemented but not yet hardware-tested (destructive on a config flash).
