Simplify (T1)(T2)x over integer bitvector types where T1 and x have the same type

[tautschnig]

When T2 has the same width (and also is a bitvector type) then the typecasts do not change the result -- we can use x directly.

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[Copilot]

Pull request overview

Adds a new bitvector-specific simplification rule to eliminate redundant “double typecasts” when the outer cast type matches the original operand type (and both cast types have the same bit-width), along with a unit test to exercise the new behavior.

Changes:

• Simplify (T1)(T2)x to x for signedbv/unsignedbv/bv types when type(x)==T1 and width(T1)==width(T2).
• Add a unit test covering the common (unsigned)(signed)x -> x case with equal widths.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
src/util/simplify_expr.cpp	Implements the new double-typecast elimination in simplify_exprt::simplify_typecast.
unit/util/simplify_expr.cpp	Adds a regression/unit test validating the new simplification behavior.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 80.47%. Comparing base (c740a89) to head (7501fca).

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #8943      +/-   ##
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- Coverage    80.47%   80.47%   -0.01%     
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  Files         1704     1704              
  Lines       188702   188721      +19     
  Branches        73       73              
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+ Hits        151854   151866      +12     
- Misses       36848    36855       +7     

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[kroening]

I would sharpen the comment/description. "Bitvector type" can be read to include things like floating-point or fixed-point numbers, for which this rule doesn't work.

The implementation seems ok, given that it specifically checks for binary and two's complement.

[tautschnig]

I would sharpen the comment/description. "Bitvector type" can be read to include things like floating-point or fixed-point numbers, for which this rule doesn't work.

Fixed comments, test name, commit message, and PR title.