[SYSTEMDS-3842] Improve test coverage of API components

[e-strauss]

This PR extends the test coverage of the API components: DMLScript (96%) and CLIOptions (99.7%).

Additionally, I identified an unreachable code fragment in the codegen SpoofCompiler and added a TODO for further investigation.

Other API components will be addressed in separate PRs.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 72.57%. Comparing base (cfbe190) to head (74ac36f).
Report is 6 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #2241      +/-   ##
============================================
+ Coverage     72.47%   72.57%   +0.10%     
- Complexity    45466    45519      +53     
============================================
  Files          1469     1469              
  Lines        170893   170896       +3     
  Branches      33325    33325              
============================================
+ Hits         123851   124036     +185     
+ Misses        37632    37471     -161     
+ Partials       9410     9389      -21     

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