TrigValSteering: Memoize path lookup and add more debug messages

This should hopefully fix ATR-21080. The slowest part of the test configuration, and therefore the unit tests, is the path lookup with find_data and get_files. Since they were called multiple times per test, the delays were multiplied. This MR adds the memoize modifier to these calls to avoid multiple lookups of the same path.

Several extra debug messages are also added to help debug such problems in the future. The time format in the logger will now also show seconds.