Fix overlaps for boundless and unknown intervals

[cmoesel]

Add special case logic for overlaps, overlaps before, and overlaps after when arguments are boundless intervals (e.g., Interval[null, null]) or unknown intervals (e.g., Interval(null, null)).

When we process an Interval that has both boundaries null, we can't infer the point type since we have no value to infer it from. This caused problems in the existing logic that needs to know the point type for some calculations. To address this, I've added special-case logic for these edge cases since we often don't really need to know the point type to arrive at the correct answer.

My CQL Long PR introduces the approach of using the resultType from the ELM when we can't easily infer types from the data. We should extend that to also work in these cases, but since we want to get this fix out ASAP, I decided to implement this approach first. We need this approach regardless since ELM does not always carry the resultType.

NOTE: The CI that runs npm audit currently fails, but the reported audit issues are currently not resolvable, so there's not much we can do.

Fixes #364.

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[codecov-commenter]

Codecov Report

❌ Patch coverage is 85.00000% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 87.69%. Comparing base (5bc96b7) to head (9dba192).

Files with missing lines	Patch %	Lines
src/datatypes/interval.ts	85.00%	0 Missing and 3 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #366      +/-   ##
==========================================
+ Coverage   87.58%   87.69%   +0.11%     
==========================================
  Files          52       52              
  Lines        4606     4624      +18     
  Branches     1297     1307      +10     
==========================================
+ Hits         4034     4055      +21     
+ Misses        359      354       -5     
- Partials      213      215       +2     

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[elsaperelli]

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