lowering: propagate snapshot pop success values in const folding

[nivanovvv]

Propagate remaining snapshot and popped value info for snapshot pop success arms, enabling follow-up snapshot pops to const-fold into known branches.

---

Note

Medium Risk
Touches compiler const-folding logic for array_snapshot_pop_front/back, which could change lowering behavior if snapshot/boxed value propagation is incorrect. Scope is limited and covered by a new regression test.

Overview
Const folding now propagates success-arm outputs for array_snapshot_pop_front/array_snapshot_pop_back: it tracks the remaining snapshot as a Snapshot(Array(..)) and tracks the popped element as a boxed snapshot value, enabling subsequent pops to be folded based on updated snapshot state.

Adds a regression test ensuring a second array_snapshot_pop_front after a successful first pop can be optimized into the known None branch by recognizing the now-empty remaining snapshot.

^{Written by Cursor Bugbot for commit ee725f8. This will update automatically on new commits. Configure here.}

[reviewable-StarkWare]

This change is