fix(gnovm): reclaim stored key object on delete() of object-keyed map

[omarsy]

Fixes #5881.

Problem

delete(m, key) on a realm map with array/struct keys detached the argument key (arg1.Deref()) from the realm via DidUpdate, not the distinct stored key object the map holds (an iv.Copy child). The stored key kept RefCount == 1, was never marked deleted, and was never removed from the store — realm storage grows across add/delete cycles and the key's storage deposit is never refunded. Deterministic (no consensus impact); the value side was already correct.

Fix

MapValue.DeleteForKey now returns the stored key TypedValue it removed; the delete builtin marks that stored key (not the argument key) in DidUpdate. DeleteForKey has a single caller, so the signature change is contained. Value handling unchanged.

Test

gnovm/tests/files/zrealm_map5.gno: init() persists a map[[1]int]int, main() deletes one entry; the finalize golden now emits d[keyOID](-213) for the reclaimed key — before the fix the map entry was dropped (u[map]) but the key object was never deleted (no d[...]). Verified red→green (the golden mismatches on unfixed code). Existing zrealm_map* / map / delete filetests pass; build + vet clean.

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[Gno2D2]

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[davd-gzl]

Looks good. Verified on e980213: reverting to mark the argument key instead of the stored key drops the d[...:8](-213) reclaim from the finalize golden, so this frees the leaked key.

Full review: https://github.com/samouraiworld/gno-agent-workspace/blob/main/reviews/pr/5xxx/5882-reclaim-stored-map-key/1-e98021315/review_claude-opus-4-8_davd-gzl.md

[davd-gzl]

DeleteForKey has the machine and could mark the removed key itself instead of returning it for the builtin. Is that deliberate, to keep DidUpdate out of MapValue?