feat: enable incremental by default

[ahabhgk]

Summary

Enable incremental by default, user can still disable it by process.env.DISABLE_RSPACK_INCREMENTAL

Related Issue

Checklist

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

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[Timeless0911]

Can you run pnpm changeset to add a minor changeset for @rspress/core?

[chenjiahan]

Can you run pnpm changeset to add a minor changeset for @rspress/core?

Changeset added in https://github.com/web-infra-dev/rspress/pull/1643/files