VSD Intervals

[thk123]

Rebased version of #5203 to see codecov report

• Each commit message has a non-empty body, explaining why the change was made.
• Methods or procedures I have added are documented, following the guidelines provided in CODING_STANDARD.md.
• The feature or user visible behaviour I have added or modified has been documented in the User Guide in doc/cprover-manual/
• Regression or unit tests are included, or existing tests cover the modified code (in this case I have detailed which ones those are in the commit message).
• My commit message includes data points confirming performance improvements (if claimed).
• My PR is restricted to a single feature or bugfix.
• White-space or formatting changes outside the feature-related changed lines are in commits of their own.

[thk123]

CI failing due to seemingly missing unit tests from the Makefile

[codecov]

Codecov Report

Merging #5354 into develop will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff            @@
##           develop    #5354   +/-   ##
========================================
  Coverage    68.04%   68.04%           
========================================
  Files         1172     1172           
  Lines        97151    97151           
========================================
  Hits         66106    66106           
  Misses       31045    31045           

Flag	Coverage Δ
#cproversmt2	42.47% <0.00%> (ø)
#regression	65.35% <0.00%> (ø)
#unit	31.94% <0.00%> (ø)

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[thk123]

On this branch I've attempted to start tidying up the interface - but this work should wait until VSD is merged, to avoid having to dive into the VSD commits and fixing them inline