fix: use outerjoin for evals filter

[RogerHYang]

resolves #4017

Caveat

Because filtering is done in SQL, logical negations require additional consideration with respect to NULL values.

For example, the logical negation of

evals["correctness"].score == 1

is actually not

evals["correctness"].score != 1

but it is instead the following

evals["correctness"].score != 1 or evals["correctness"].score is None

This is because NULL != 1 is actually false in SQL.

[axiomofjoy]

Great job