🐛 Replace runtime-dependent memory admission in makeSlice with deterministic quota

[ccamel]

Summary

makeSlice (engine/malloc.go:21-42) currently bases its allocation gate on debug.SetMemoryLimit(-1) and runtime.ReadMemStats, then compares the reported "free" bytes against the requested slice length. Go's allocator and GC are non-deterministic; two replicas can observe different stats.Sys or stats.HeapReleased, so one node may reject the allocation with errOutOfMemory while another succeeds. That divergence breaks determinism.

Why it matters

Any predicate that allocates via makeSlice (e.g., copy_term/2, setof/3, list/dict helpers) can yield different outcomes across validators. On a blockchain this can fork consensus.