Add tests for hash collisions

[alamb]

Which issue does this PR close?

Closes #841

Rationale for this change

1. The hash implementation in ahash::RandomState is very good, and thus it is very hard to cause hash collisions in tests
2. Since it is hard to cause hash collisions, it means we do not have test coverage of this case. This is a problem because checking for hash collisions is often required in the performance critical section of code and thus prone to being optimized out

What changes are included in this PR?

1. Add a (off by default) feature flag that forces hash collisions
2. Add a CI test that runs queries using those flags
3. Updates tests to pass, and filed tickets for those that did not

Are there any user-facing changes?

No

[Dandandan]

Cool approach!
I am wondering if we can keep this in all test cases as for bigger joins / aggregates it could slow it down significantly.

Also we might want to add some explicit test for the problem (might be null-related? #843 (comment)) later.

[jorgecarleitao]

Really neat and long-lasting approach!