Byte operator lowering: additional preconditions in instantiate_byte_…

[tautschnig]

…array

No code changes, just additional safety checks to guard against
implementation errors: instantiate_byte_array requires a byte array or
vector typed source operand. Other kinds of arrays/vectors are not
supported or expected.

• 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.

[codecov]

Codecov Report

Merging #6487 (3008132) into develop (5bf69a3) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff            @@
##           develop    #6487   +/-   ##
========================================
  Coverage    76.04%   76.04%           
========================================
  Files         1546     1546           
  Lines       165521   165523    +2     
========================================
+ Hits        125864   125866    +2     
  Misses       39657    39657           

Impacted Files	Coverage Δ
src/solvers/lowering/byte_operators.cpp	92.23% <100.00%> (+0.01%)	⬆️

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[martin-cs]

I like PRs like this!