Use Complete Access instead of writing single subindexes

[kraemr]

Currently all the Configuration happens with single index sdo writes.
This is really really expensive due to how sdo writes function ...
Each sdo write requires some time for the write to reach the EEPROM during which it is busy.
While the EEPROM is busy state change to PREOP-PDI or other initialization/State based reads or writes will timeout.

The Fix:
Use Complete Access for Configuration of all Terminals (if available, some might not have it)
We can just map the struct layout to the layout of the subindices in the EEPROM, but for that the struct MUST
be tagged with repr(c) and it must be packed, so that it matches EXACTLY without padding bytes what the layout is.

Of course ethercrab has no example where it shows how this works or even if it is supported :)