Update CaDiCaL from 1.4.1 to 1.5.3

[tautschnig]

Maintenance update to the latest release, no notable performance differences expected or observed.

Also patch out the comparison of this against NULL, which we reported upstream as arminbiere/cadical#54.

Fixes: #7725

• 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.

[codecov]

Codecov Report

Patch and project coverage have no change.

Comparison is base (d5e13f1) 78.54% compared to head (f9cd820) 78.54%.

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #7734   +/-   ##
========================================
  Coverage    78.54%   78.54%           
========================================
  Files         1688     1688           
  Lines       193001   193001           
========================================
  Hits        151599   151599           
  Misses       41402    41402           

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