Refactor pb_solver to use structured bindings for wliteral patterns (#8391)

* Initial plan

* Refactor pb_solver.cpp to use C++17 structured bindings for wliteral patterns

Co-authored-by: NikolajBjorner <3085284+NikolajBjorner@users.noreply.github.com>

* Fix active2wlits to avoid unnecessary wliteral reconstruction

Co-authored-by: NikolajBjorner <3085284+NikolajBjorner@users.noreply.github.com>

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Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: NikolajBjorner <3085284+NikolajBjorner@users.noreply.github.com>

Author: Copilot