docs: add npm bundle size badge

[BuptStEve]

Before submitting the PR, please make sure you do the following

• Read the Contributing Guidelines.
• Check that there isn't already a PR that solves the problem the same way to avoid creating a duplicate.
• Provide a description in this PR that addresses what the PR is solving, or reference the issue that it solves (e.g. close #123).
• Ideally, include relevant tests that fail without this PR but pass with it.

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Description

Additional context

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copilot:summary

copilot:walkthrough