Fix type conversion operator tests for malformed inputs. Enable tests for Boolean and null literals.

[antvaset]

• Fixing the ToInteger(String), ToDateTime(String), ToTime(String) tests for malformed string arguments (see spec for ToInteger, ToDateTime, ToTime).
• Enabling the Boolean and null literal tests (key change at https://github.com/antvaset/clinical_quality_language/commit/d4dd873ba41239f366e187ac00f2ec47acb61288#diff-223279de96f0d1e72a0e8cf595773009f4668f46512388a3b6f9f7ad404749d2R147).

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 62.26%. Comparing base (e00c396) to head (529a2f8). Report is 3 commits behind head on master.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #1371 +/- ## ============================================ - Coverage 62.26% 62.26% -0.01% - Complexity 6951 6953 +2 ============================================ Files 492 492 Lines 27727 27731 +4 Branches 5506 5508 +2 ============================================ + Hits 17265 17266 +1 - Misses 8198 8200 +2 - Partials 2264 2265 +1 ```

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[JPercival]

@brynrhodes - Bump