Add mocks

[Lana243]

Summary:

Checklist:

• The PR addresses a single issue. If it can be divided into multiple independent PRs, please do so.
• The PR is divided into a logical sequence of commits OR a single commit is sufficient.
• There are no unnecessary commits (e.g. commits fixing issues in a previous commit in the same PR).
• Each commit has a meaningful message documenting what it does.
• All messages added to the codebase, all comments, as well as commit messages are spellchecked.
• The code is commented OR not applicable/necessary.
• The patch is formatted via clang-format OR not applicable (if explicitly overridden leave unchecked and explain).
• There are test cases for the code you added or modified OR no such test cases are required.

[codecov-commenter]

Codecov Report

Merging #80 (0f1640e) into main (e9dc5f3) will increase coverage by 0.00%.
The diff coverage is 64.86%.

❗ Current head 0f1640e differs from pull request most recent head 6f91181. Consider uploading reports for the commit 6f91181 to get more accurate results

@@           Coverage Diff            @@
##             main      #80    +/-   ##
========================================
  Coverage   65.12%   65.13%            
========================================
  Files         209      211     +2     
  Lines       28462    28861   +399     
  Branches     6335     6424    +89     
========================================
+ Hits        18537    18798   +261     
- Misses       7425     7527   +102     
- Partials     2500     2536    +36     

Files Changed	Coverage Δ
include/klee/Expr/IndependentSet.h	56.66% <ø> (ø)
lib/Core/ExecutionState.cpp	73.91% <ø> (ø)
lib/Core/Executor.h	76.92% <ø> (ø)
lib/Core/SpecialFunctionHandler.h	0.00% <ø> (ø)
lib/Expr/Parser.cpp	55.11% <0.00%> (-1.66%)	⬇️
runtime/Mocks/models.c	0.00% <0.00%> (ø)
lib/Core/SpecialFunctionHandler.cpp	72.48% <30.00%> (-0.98%)	⬇️
lib/Expr/ExprPPrinter.cpp	88.56% <30.00%> (-1.47%)	⬇️
tools/klee/main.cpp	58.20% <51.85%> (-0.93%)	⬇️
lib/Expr/IndependentSet.cpp	77.11% <63.63%> (-0.90%)	⬇️
... and 10 more

... and 2 files with indirect coverage changes

[misonijnik]

#109 PR incorporates this PR but also advances further.