refactor: modernize react refresh runtime helpers

[chenjiahan]

Summary

• modernize the react refresh client/runtime helpers with const, arrow functions, template literals, and simpler control flow
• preserve the previous runtime behavior for async export handling and __esModule-only refresh boundaries while cleaning up the implementation

Testing

• pnpm test

Related Links

• None

[Copilot]

Pull request overview

This PR modernizes the React Refresh client/runtime helper code while aiming to preserve existing runtime behavior (notably around async exports and refresh boundary detection).

Changes:

• Refactors refresh helpers to use const/let, arrow functions, template literals, and simplified control flow.
• Keeps existing refresh boundary/signature logic intact while reducing boilerplate in shouldInvalidateReactRefreshBoundary and HMR handlers.
• Minor style/consistency updates in the React Refresh entry/runtime wiring.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 3 comments.

File	Description
client/refreshUtils.js	Refactors module export extraction, boundary signature/invalidation, debounce update helper, and HMR dispose/accept handlers.
client/reactRefreshEntry.js	Modernizes safeThis/global detection and injected-flag string building.
client/reactRefresh.js	Simplifies refresh execution path and test-mode resolution while preserving Promise vs non-Promise export handling.

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