Add option to stop search once a solution is found

[AustinT]

Rationale: Even though our main use case for syntheseus so far has been to run search for a fixed amount of time and analyze all routes in the resulting search graph, there are some scenarios where we only care about whether or not a route is found (e.g. benchmarking). This is pretty simple to check so I thought it is worth supporting.

Implementation: previously all algorithms called time_limit_reached each iteration to decide whether to stop early. I just augmented this function to also check for stopping once a solution is found. This involved:

1. Adding a stop_on_first_solution kwarg to the base algorithm class (defaults to False, which is the most sensible default in my opinion)
2. Adding logic to time_limit_reached which checks self.stop_on_first_solution and graph.root_node.has_solution. This required adding a graph argument to the function (previously it took no arguments), causing changes in all algorithm files.
3. Because of this added functionality, time_limit_reached no longer seemed like a descriptive name for the function, so I changed it to should_stop_search
4. I added a test to syntheseus/tests/search/algorithms/test_base.py which tests the effectiveness of this kwarg for all algorithms (because algorithm-specific tests all subclass the base test)

Rejected alternative: although it would be appealing to generalize this to "stop after n solutions" or "stop after n diverse solutions" this is not simple or quick to check so I don't think we should support it out-of-the-box. If users want this then they could implement it themselves in a subclass.

[AustinT]

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[kmaziarz]

there are some scenarios where we only care about whether or not a route is found (e.g. benchmarking)

Can you elaborate on this usecase?

[kmaziarz]

LGTM!

[AustinT]

there are some scenarios where we only care about whether or not a route is found (e.g. benchmarking)

Can you elaborate on this usecase?

For example, if you wanted to reproduce the experiment in the retro* / PDVN paper, or make a box plot of the time at which the first solution is found, this only requires finding on solution (that is all they report). The students I am working with are trying to evaluate value functions in terms of how quickly they guide a search algorithm to a solution. That is another use case. Does that make sense?