post-order traversal range for expressions

[kroening]

• Adds const_post_depth_iteratort for post-order depth-first traversal of expressions
• Adds const_post_depth_iterator_range_adaptert and post_traversal() function for range-based for loops

This complements the existing pre-order pre_traversal() from #8819

• 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.
• 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).
• n/a 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.

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 80.00%. Comparing base (35fbe06) to head (199d931).
⚠️ Report is 2 commits behind head on develop.

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #8822   +/-   ##
========================================
  Coverage    80.00%   80.00%           
========================================
  Files         1700     1700           
  Lines       188285   188332   +47     
  Branches        73       73           
========================================
+ Hits        150632   150679   +47     
  Misses       37653    37653           

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