Speedup of canPassThrough() method

[JackRainy]

I have been playing with JProfiler (amasing tool, btw! Unfortunately, I cannot afford it for myself) and found out that canPassThrough() method - the most frequent called method can be optimized and speed up.

Preliminary investigation:
canPassThrough() method calls canEnterTiles() which calls isAtWarWith() and it takes almost 50% of its own time. Another 49% of the time is spent for HashMap contains checks of the uniques.

I did refactoring of those two methods: canEnterTiles() does not call isAtWarWith() anymore, but uses its checks directly. Also, isAtWarWith() does not get diplomacy manager twice. That's has given quite good throughput already.

Furthermore, I removed one more redundant check isEmpty: method first() does a check isEmpty inside, so no need to call isNotEmpty before it.

And lastly, I used the same trick as we use in other places - caching of the MapUnit uniques as boolean flags - it also gave some portion of speed boost.

Results:

Test set	Before	After	Boost
Test set 1	15-16 sec	11-13 sec	19-27%
Test set 2	12.5 sec	10-12 sec	4-20%

Summing up: canPassThrough() is almost 20% faster now!

And of course, I did 100% unit test coverage for the method before introducing any changes.

[yairm210]

Amazing!!!
I cannot tell you how much time I have spent on improving the performance of the basic movement functions, it's great to see that there's always room for more improvement ❤️