Byte-operator lowering: do not unconditionally insert bv cast

[tautschnig]

In 848e633 a cast to bv was inserted to block interpreting floatbv type casts from taking place. It was unnecessarily inserted for all bitvector types. While this does not result in wrong semantics, it may block simplification for happening when we end up (via other simplifier rules) creating a bv (and not (un)signed bv) typed constant. All of these transformations are correct, but we may end up with an equality over pointer-typed constants where the underlying constant is a(n) (un)signed bv on one side, and a bv on the other side. The bit patterns match, so the back-end will correctly solve this, but the simplifier cannot.

Observed when studying
model-checking/kani#1978.

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[peterschrammel]

Is this covered by tests?

[tautschnig]

Is this covered by tests?

Should be covered by unit/solvers/lowering/byte_operators.cpp, but I've rebased and will seek confirmation by Codecov.

[codecov]

Codecov Report

Patch coverage: 100.00% and no project coverage change

Comparison is base (a4989b9) 78.50% compared to head (f67691e) 78.50%.

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #7571   +/-   ##
========================================
  Coverage    78.50%   78.50%           
========================================
  Files         1670     1670           
  Lines       191760   191763    +3     
========================================
+ Hits        150540   150544    +4     
+ Misses       41220    41219    -1     

Impacted Files	Coverage Δ
src/util/lower_byte_operators.cpp	92.86% <100.00%> (+0.01%)	⬆️
src/util/simplify_expr.cpp	85.36% <0.00%> (+0.06%)	⬆️

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