Stop generating all prover call at once

Instead of generating all prover calls (which can be lengthy on setups with a lot of processes used by default) in a timeout, we generate only one in an idle call (which is called more often). The expected result is to avoid freezing of the IDE when the user has a lot of processors.

Use prio of 300 for the idle call: from testing, using less than 100 take priority over GTK (resulting in freezing).

Renaming timeout_handler to idle_handler