CONTRACTS: ensure at most one predicate per pointer

[remi-delmas-3000]

Please ignore the first commit, it is from #8576 and will disappear when rebasing.

Fixes a discrepancy between assert and assume behaviour for pointer predicates, by ensuring
that at most one predicate occurrence can be established at all times, in both assume and assert
contexts.

Before, is_fresh(p, n) && is_fresh(p, n) would fail in assert contexts but pass in assume contexts
by allocating twice.

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• 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.
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[codecov]

Codecov Report

Attention: Patch coverage is 82.05128% with 7 lines in your changes missing coverage. Please review.

Project coverage is 78.85%. Comparing base (3d79560) to head (42af48e).

Files with missing lines	Patch %	Lines
.../contracts/dynamic-frames/dfcc_wrapper_program.cpp	70.00%	6 Missing ⚠️
...strument/contracts/dynamic-frames/dfcc_library.cpp	93.75%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #8577      +/-   ##
===========================================
- Coverage    78.92%   78.85%   -0.07%     
===========================================
  Files         1732     1732              
  Lines       198953   199119     +166     
  Branches     18560    18560              
===========================================
+ Hits        157021   157023       +2     
- Misses       41932    42096     +164     

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