Per gballet's comment 3101751325 on PR #34055: the *Single functions
are essentially the same thing as *ValuesAtStem with one slot set. The
original design dispatched through *ValuesAtStem for dedup; this commit
restores that shape on the arena side.
- GetValue now delegates to GetValuesAtStem and indexes the returned
256-slot array header (no allocation — the stem node returns its own
inline values array as a slice).
- InsertSingle now builds a stack-allocated [StemNodeWidth][]byte with
only the target slot set and delegates to InsertValuesAtStem.
- Delete the insertSingleInternal tree walker (~90 LOC) and the whole
splitStemInsert (~60 LOC) — the *ValuesAtStem / splitStemValuesInsert
pair already handles every case.
Addresses gballet comments 3101751325, 3101739001, 3101724199, 3101721238
(the last three subsumed by the consolidation — the duplicated helper
bodies no longer exist).
Net: ~150 LOC removed from store_ops.go. Allocation cost for InsertSingle
is bounded by the stack-allocated 256-slot array (one stack frame, no
heap allocation on the hot path).
33227e7e6d