Add edge case regression tests for --generate-function-body const handling

[tautschnig]

The existing tests provided basic const handling coverage, but several complex scenarios were not comprehensively tested. This PR addresses the following edge cases:

1. Triple pointer const handling - int * const ** (const at middle level)
2. Double const qualification - const int * const (both pointer and data const)
3. Array of pointers to const - const int ** / const int *arr[]
4. Const function pointers - func_ptr_t * const
5. Nested struct const pointers - Mixed const/non-const in nested structures
6. Combined qualifiers - volatile const int * (volatile + const interaction)
7. Const array parameters - const int[] (array parameter const protection)
8. Pointer to const struct - const struct test_struct * (struct-level const)
9. Systematic const variations - Comprehensive test of const at each pointer level

Co-authored-by: Kiro autonomous agent

Fixes: #1948

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• 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).
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• My PR is restricted to a single feature or bugfix.
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[Copilot]

Pull request overview

Adds regression coverage for --generate-function-body around tricky const/volatile qualifier placement, especially across multi-level pointers, arrays, structs, and function-pointer indirections.

Changes:

• Introduces new regression test directories covering volatile+const, const at different pointer levels, and const in structs/arrays.
• Adds systematic “pointer variations” test that mixes const placement across **/* const */** const forms.
• Adds negative tests (expected assertion failures) where pointer relationships are allowed to change.

Reviewed changes

Copilot reviewed 18 out of 18 changed files in this pull request and generated 11 comments.

Show a summary per file

File	Description
regression/goto-instrument/generate-function-body-volatile-const-pointers/test.desc	New harness expectations for volatile+const pointer test
regression/goto-instrument/generate-function-body-volatile-const-pointers/main.c	Adds volatile+const pointer regression scenario
regression/goto-instrument/generate-function-body-triple-pointer-const-middle/test.desc	New harness expectations for middle-level const triple pointer test
regression/goto-instrument/generate-function-body-triple-pointer-const-middle/main.c	Adds triple-pointer “const in middle” regression scenario
regression/goto-instrument/generate-function-body-pointer-variations-const/test.desc	Adds multi-variant const pointer-level expectations
regression/goto-instrument/generate-function-body-pointer-variations-const/main.c	Implements const-placement matrix for pointer-to-pointer cases
regression/goto-instrument/generate-function-body-pointer-to-const-struct/test.desc	New harness expectations for pointer-to-const-struct test
regression/goto-instrument/generate-function-body-pointer-to-const-struct/main.c	Adds regression scenario for const-qualified struct pointer
regression/goto-instrument/generate-function-body-nested-struct-const-pointers/test.desc	New harness expectations for nested struct const-pointer test
regression/goto-instrument/generate-function-body-nested-struct-const-pointers/main.c	Adds nested struct scenario mixing const and non-const pointers
regression/goto-instrument/generate-function-body-function-pointer-const/test.desc	Adds expected-failure harness for const function-pointer indirection
regression/goto-instrument/generate-function-body-function-pointer-const/main.c	Adds function-pointer constness regression scenario
regression/goto-instrument/generate-function-body-const-pointer-to-const/test.desc	New harness expectations for const int * const
regression/goto-instrument/generate-function-body-const-pointer-to-const/main.c	Adds double-const pointer regression scenario
regression/goto-instrument/generate-function-body-const-array-parameter/test.desc	New harness expectations for const array parameter
regression/goto-instrument/generate-function-body-const-array-parameter/main.c	Adds const array parameter regression scenario
regression/goto-instrument/generate-function-body-array-of-pointers-to-const/test.desc	Adds expected-failure harness for array-of-pointers-to-const
regression/goto-instrument/generate-function-body-array-of-pointers-to-const/main.c	Adds array-of-pointers-to-const regression scenario

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 80.01%. Comparing base (b191cc1) to head (699a625).

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #8797   +/-   ##
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  Coverage    80.01%   80.01%           
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  Files         1700     1700           
  Lines       188345   188345           
  Branches        73       73           
========================================
  Hits        150696   150696           
  Misses       37649    37649           

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