fix(hir): nested local must not reuse a module const's forward-declared id (#1758/#321)

[proggeramlug]

Summary

A nested local binding could reuse a module-level const/let's
forward-declared LocalId, conflating two distinct variables.

The module-level forward-declaration pass pre-registers a LocalId for each
module-level const/let (so forward references resolve). The var-decl
lowering reused that pre-registered id for any binding of the same name —
including a nested local inside a function body:

const merge = (s, t) => zipWith(s, t);        // forward-refs module zipWith
function helper() { const zipWith = 5; ... }   // local shadow (declared first)
const zipWith = (a, b) => a + b;               // module const

helper's local zipWith consumed the module var's pre-registered id, so the
local and the module binding shared one id; the real zipWith function landed
on a fresh id; and merge's closure — which forward-resolved zipWith to the
pre-registered id — pointed at the wrong (uninitialised) slot →
TypeError: value is not a function. Order-dependent: only triggers when the
local shadow precedes the module const.

Why it matters — unblocks the effect barrel

import { Effect } from "effect" threw value is not a function in
TestContext.ts init. effect's layer.merge = dual(2, (self, that) => zipWith(self, that, ...)) references the module zipWith (exported at
internal/layer.ts:1191), and a local zipWith (L1180, inside another
function) precedes it — exactly this shape.

Localization

Probed pipe args (all defined) → narrowed to layer.merge(a,b) throwing →
merge's body calls zipWith(self,that,cb) (the 3-arg js_closure_call3 in
the backtrace) → HIR showed merge body Call{callee: LocalGet(1)} while the
module zipWith is Let id:6 (id 1 = the shadow). An env-gated define_local
trace confirmed only two zipWith define_locals (both scope_depth=0) — the
nested local made none; it reused.

Fix

Gate the pre_registered_module_vars id-reuse (both the simple-ident and
destructuring-fallback sites in destructuring/var_decl.rs) on module scope
(scope_depth == 0 && inside_block_scope == 0), mirroring define_local's own
module-level tagging. A nested local of the same name now gets a fresh id.

Validation

• New gap test test_gap_module_const_local_shadow.ts (core shape +
  dual-indirection + independent-nested-local guard) — byte-identical to node.
• Full 578-test regression sweep (PERRY_NO_AUTO_OPTIMIZE=1): 0
  regressions — all 39 failures + 4 hangs fail/hang identically on the
  pre-fix baseline (decorators / crypto / fastify / sqlite / fs / date /
  class-field-layout / mixins — all pre-existing).
• With this + fix(codegen): namespace-member access of a renamed class export (#1758) #1812 (renamed-class-export, in review), the full effect
  framework works end-to-end, byte-identical to node:
  effect/Effect deep import → 42, effect/Schema init → ok,
  effect/Schema decode → "hello", and the import { Effect } from "effect"
  barrel → 42 (Effect.runSync(Effect.succeed(42))).

Refs #1758, #321, #1785, #1772, #1791.