Avoid branches in CPROVER library for --paths mode

[tautschnig]

Replace if-statements with conditional expressions in two places in the built-in CPROVER library to avoid generating GOTO branches that cause exponential path explosion in --paths mode:

1. __CPROVER_deallocate: nondeterministic deallocation tracking
   Before: if(__VERIFIER_nondet___CPROVER_bool()) __CPROVER_deallocated = ptr;
   After: __CPROVER_deallocated = nondet ? ptr : __CPROVER_deallocated;

2. free: memory leak detection
   Before: if(__CPROVER_memory_leak==ptr) __CPROVER_memory_leak=0;
   After: __CPROVER_memory_leak = (leak==ptr) ? 0 : leak;

Both are semantically equivalent but avoid GOTO instructions, so --paths mode does not fork at these points.

Impact on Collections-C benchmark (159 tests, --paths lifo):
Original --paths: 61 pass, 93 timeout, 3105s
After fix 1: 123 pass, 31 timeout, 1463s
After both fixes: 127 pass, 26 timeout, 1159s
With precomp: 127 pass, 26 timeout, 1046s (14x vs Soteria)

The fixed --paths mode now passes 9 MORE tests than monolithic SAT (127 vs 118), including treeset and treetable tests.

• Each commit message has a non-empty body, explaining why the change was made.
• n/a Methods or procedures I have added are documented, following the guidelines provided in CODING_STANDARD.md.
• n/a 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.
• n/a White-space or formatting changes outside the feature-related changed lines are in commits of their own.

[Copilot]

Pull request overview

This PR updates the built-in ANSI-C CPROVER library (stdlib.c) to avoid generating GOTO-level control-flow branches in --paths mode by replacing two if statements with conditional (?:) expressions. This targets path explosion by keeping the logic as expression-level conditionals instead of control-flow splits.

Changes:

• Rewrite free’s memory-leak tracking (__CPROVER_memory_leak) update using a conditional expression.
• Rewrite __CPROVER_deallocate’s nondeterministic deallocation tracking (__CPROVER_deallocated) update using a conditional expression.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 80.50%. Comparing base (b32074b) to head (8c2786d).

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #8971   +/-   ##
========================================
  Coverage    80.50%   80.50%           
========================================
  Files         1704     1704           
  Lines       188778   188778           
  Branches        73       73           
========================================
+ Hits        151975   151978    +3     
+ Misses       36803    36800    -3     

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