chore(react-overflow): unify noop callbacks via a shared noop constant

- overflowContext.ts: replace the inline `() => () => null` / `() => null`
  default no-ops on the context value with references to a local `noop` const
  (block-form body).
- useOverflowContainer.ts: `defaultSubscribe` now returns the same shared
  `noop` rather than re-allocating a fresh placeholder per call.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: bsunderhus

packages/react-components/react-overflow/library/src/overflowContext.ts

@@ -37,20 +37,24 @@ export const OverflowContext = React.createContext<OverflowContextValue | undefi
   undefined,
 ) as React.Context<OverflowContextValue>;
 
+const noop = () => {
+  /* noop */
+};
+
 const overflowContextDefaultValue: OverflowContextValue = {
   hasOverflow: false,
   itemVisibility: {},
   groupVisibility: {},
-  registerItem: () => () => null,
-  updateOverflow: () => null,
-  registerOverflowMenu: () => () => null,
-  registerDivider: () => () => null,
+  registerItem: () => noop,
+  updateOverflow: noop,
+  registerOverflowMenu: () => noop,
+  registerDivider: () => noop,
   getSnapshot: () => ({
     visibleItems: [],
     invisibleItems: [],
     groupVisibility: {},
   }),
-  subscribe: () => () => null,
+  subscribe: () => noop,
 };
 
 /**