Improved testing for "max intervals" (Interval[null, null]) and "unknown intervals" (Interval(null, null))

[brynrhodes]

Fixed #106

[bryantaustin13]

The following tests have unmatched actual vs expected results. If that is as it should be, due to clinical_quality_language errors, then I am willing to approve. I am willing to enter issues into the cql repo.

If Interval[null, null] actually means Interval[minimum value, maximum vale] then that explains many of the expected values.

TestMaxIntervalEndsFalse returns null, but expected is false
Interval[1, 10] ends Interval[null, null]
https://cql.hl7.org/09-b-cqlreference.html#ends
should be false supported by the Ends, Start, and End operator definitions in above link
TestIntegerInMaxIntervalTrue returns false, but expected is true
5 in Interval[null, null]
https://cql.hl7.org/09-b-cqlreference.html#in
5 >= null → treated as true (closed null boundary)
5 <= null → treated as true (closed null boundary)
TestIntegerInUnknownIntervalNull returns false, but expected is null
5 in Interval(null, null)
https://cql.hl7.org/09-b-cqlreference.html#in
5 > null
5 < null
treated as null
TestMaxIntervalOverlapsTrue returns null, but expected is true
TestMaxIntervalOverlapsBeforeTrue returns null, but expected is true
TestMaxIntervalOverlapsAfterTrue returns null, but expected is true
TestPointFromMaxIntervalError has no expected output
TestMaxIntervalStartsFalse returns null, but expected is false
TestUnionMaxInterval returns null, expected is Interval[null, null]

[brynrhodes]

Correct, I believe the expected outcomes here are correct, and if an engine isn't getting these results, it needs to be corrected.