Connect let-bound arrays to originals in array theory

[tautschnig]

When a let expression binds a variable to an array value, the fresh symbol and the original array are disconnected in the array theory's union-find. This means Ackermann constraints and element-wise equality constraints don't propagate between them, causing spurious counterexamples in smt2_solver.

Fix: in convert_let, for array-typed bindings with unbounded array type, call record_array_equality to create an element-wise equality between the fresh variable and the bound value, and assert it as true. This connects the two representations so the array theory generates proper constraints.

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[Copilot]

Pull request overview

This PR fixes missing propagation in the unbounded-array theory when arrays are introduced via let bindings, by explicitly connecting the fresh let-bound array symbol to the original array expression so array constraints (Ackermann + extensional equality) propagate correctly in smt2_solver.

Changes:

• In boolbvt::convert_let, record and assert an array equality between fresh let-bound symbols and their bound values for unbounded array types.
• Add a new smt2_solver regression test descriptor for let-bound arrays.

Reviewed changes

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

File	Description
src/solvers/flattening/boolbv_let.cpp	Records/asserts array equalities for unbounded array let-bindings to connect union-find classes in array theory.
regression/smt2_solver/let-array/let-array.desc	Adds a regression descriptor intended to check the corrected let/array-theory interaction.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 80.47%. Comparing base (582cc2a) to head (14105d5).
⚠️ Report is 2 commits behind head on develop.

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #8942   +/-   ##
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  Coverage    80.47%   80.47%           
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  Files         1704     1704           
  Lines       188749   188762   +13     
  Branches        73       73           
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+ Hits        151892   151905   +13     
  Misses       36857    36857           

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