Use most recent SearchSettings in new debugger

[gnanabite]

For searches that use one-off SearchSettings, the searchSettings field of the BaseJUnitTest won't have the required information. For example, see initView of lab 2: since we're using the settings in the BaseJUnitTest, the debugger will open but there won't be any settings.

The fix is to save the settings used in the last search, similar to https://github.com/emichael/dslabs/pull/20#discussion_r803341651; this time we need to save the settings from both BFS and DFS.

Tested:

• repeated the prune pane test from https://github.com/emichael/dslabs/pull/29.
• modified the ViewServer to never add a backup even if there was an idle server available, and ensured that the correct prunes and goals are shown when the test fails on initView.
• modified the ViewServer to handle acknowledgements incorrectly, and confirmed that when lab 2 part 2 test 20 fails, the debugger shows that the invariant is violated

[emichael]

LGTM! Once I get around to merging feature/save-traces, we should probably clone the settings to defend against the settings changing after the search but before assertGoalFound gets invoked. It's not necessary, though.