fix: extract more Nats in extractClosed (#8535)

This PR extracts more Nats (and their downstream users) in extractClosed
by fixing a silly oversight in the logic.

src/Lean/Compiler/LCNF/ExtractClosed.lean

@@ -63,7 +63,7 @@ partial def shouldExtractLetValue (isRoot : Bool) (v : LetValue) : M Bool := do
   | .lit (.nat v) =>
     -- The old compiler's implementation used the runtime's `is_scalar` function, which
     -- introduces a dependency on the architecture used by the compiler.
-    return v >= Nat.pow 2 63
+    return !isRoot || v >= Nat.pow 2 63
   | .lit _ | .erased => return !isRoot
   | .const name _ args =>
     if (← read).sccDecls.any (·.name == name) then