perf(hmr): no need to get assets info

[chenjiahan]

Summary

When using stats.toJson in Rspack, enabling the assets: true option introduces noticeable Rust-JS communication overhead — typically a few milliseconds for small applications, but potentially several hundred milliseconds for large ones.

This PR avoids that overhead by checking stats.hash instead of relying on asset.emitted.

Before

After

Related Links

• fix: perf webpack/webpack-dev-server#3906

Checklist

• Tests updated (or not required).
• Documentation updated (or not required).

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[Copilot]

Pull Request Overview

This PR optimizes Hot Module Replacement (HMR) performance by eliminating the need to retrieve asset information during stats processing. Instead of checking asset.emitted to determine if files have changed, it now tracks build hashes to detect changes, reducing Rust-JS communication overhead.

• Introduces hash-based change detection using a Map to store previous build hashes
• Removes dependency on asset information (assets: true) from stats options
• Optimizes the condition for skipping HMR updates when no changes are detected

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