Factor out Oxide image handling from here and Hubris into a common no_std library

[lzrd]

Hubtools and Hubris have overlap in their implementations of Hubris/Bootleby image handling that
should be combined into a no_std crate so that there is one source of truth.
This may be limited to the read-only image handling which would be used here and in:
hubris: drv/lpc55-update-server/src/image.rs
hubris: lib/rot-startup/src/image.rs

[lzrd]

Tests would also be required.