Split inspector::is_pending() in two logical parts

Split inspector::is_pending() in two logical parts

- get_max_consider() returns how many times this simcall should be considered.
- prepare() does what needs to be done for the simcall to be fired in user space

This removes the RPC from MC to App to get this information:

 - The value of get_max_consider() is copied in the simcall structure
   when the AppSide prepares to wait for new instructions from the MC.
 - prepare() was already called by handle_simcall() on AppSide, to
   obey trace replays.

Less RPC is faster and less eror prone.