add cli commands for reading/writing flash indexes
- `diii flash-read 2` -- prints out flash index 2
- `diii flash-read 2 > pset2.txt` -- outputs text to file `pset2.txt`
- `diii flash-write 3 pset2.txt` -- writes `pset2.txt` to index 3
note: flash max size per index is 4k
note: requires firmware `250220`