Add RPC calls to the log

This is a feature request.

Currently if you make an RPC call this is not logged in the log that is accessible through semi-hosting. This would be very useful though to monitor what is going on between the boxes, even if it's just the calls (serialized values would be even nicer, but that's hard).

No files or tests are named. Start by locating the RPC implementation and the semihosting-accessible logging path, then determine where calls between boxes can be recorded without serializing values. Done means RPC calls appear in that log; confirm the expected format and coverage before changing code.

Written by the indexing model from the issue text.