internal timing of transient F-stat map function

For TransientGridSearch class, saves an internal attribute that adds up timing of all calls to call_compute_transient_fstat_map(). Also printed out (on info level) at the end, I might change that to debug at a later point, but info is good for me at the moment.

@GregAshton Pipeline failed as usual while you're offline, so please give it a 2nd try.