Make namespacet references const where possible

[tautschnig]

namespacet has no non-const member functions (other than constructors and assignment), so non-const references to it are misleading. The only legitimate non-const use is in goto_symext::symex_with_state where the namespacet object is reassigned via reset_namespacet.

Changes in src/:

• linking_diagnosticst constructor: namespacet& -> const namespacet& (the member was already const)
• cfg_visitort (wmm): namespacet& member and constructor parameter made const

Changes in unit/:

• variable_sensitivity_test_helpers: all namespacet& parameters -> const
• eval-member-access, assume, assume_prune, maximum_length, extremes-go-top: all namespacet& parameters and members -> const

• 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).
• 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.

[Copilot]

Pull request overview

This PR improves const-correctness by converting namespacet & parameters/members to const namespacet & in core code and variable-sensitivity unit tests, aligning the API with the fact that namespacet is effectively immutable after construction.

Changes:

• Make linking_diagnosticst constructor accept const namespacet &.
• Update WMM cfg_visitort to store a const namespacet &.
• Update multiple variable-sensitivity unit-test helpers/tests to take/store const namespacet &.

Reviewed changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
unit/analyses/variable-sensitivity/variable_sensitivity_test_helpers.h	Update helper function signatures to const namespacet &.
unit/analyses/variable-sensitivity/variable_sensitivity_test_helpers.cpp	Keep helper definitions in sync with const namespacet & signatures.
unit/analyses/variable-sensitivity/value_expression_evaluation/assume_prune.cpp	Update helper functions to accept const namespacet &.
unit/analyses/variable-sensitivity/value_expression_evaluation/assume.cpp	Make assume_testert store const namespacet & and update related helpers.
unit/analyses/variable-sensitivity/interval_abstract_value/extremes-go-top.cpp	Update helper signature to const namespacet & (and reflow declaration).
unit/analyses/variable-sensitivity/full_array_abstract_object/maximum_length.cpp	Update write_array helper signature to const namespacet &.
unit/analyses/variable-sensitivity/eval-member-access.cpp	Update helper prototypes/definitions to const namespacet &.
src/linking/linking_diagnostics.h	Make linking_diagnosticst ctor take const namespacet &.
src/goto-instrument/wmm/goto2graph.h	Make cfg_visitort::ns a const namespacet &.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 80.51%. Comparing base (6d1956b) to head (954ca7b).
⚠️ Report is 6 commits behind head on develop.

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #8995   +/-   ##
========================================
  Coverage    80.50%   80.51%           
========================================
  Files         1704     1704           
  Lines       188818   188821    +3     
  Branches        73       73           
========================================
+ Hits        152017   152022    +5     
+ Misses       36801    36799    -2     

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