Name and order the turn loop code

Every package-level name that only the turn loop uses starts with turn:
the loop is TurnLoop, its function call items are TurnFunctionCall and
TurnFunctionCallOutput, and its error of a log write is errTurnLogWrite.
Event stays generic, because the daemon, the terminal client, and the
Telegram bot read the events too.

The declarations of the turn files follow the order of the go-code
skill. The behavior does not change.

Issue: 947bddb