feat!: switch to named RspackChain export

[chenjiahan]

Summary

• replace the package default export with a named RspackChain export so the runtime entry point and public types expose the same API shape
• update the README examples plus runtime and type tests to use import { RspackChain } from 'rspack-chain'

Testing

• pnpm test
• pnpm test:types
• pnpm build

Related Links

• None

[Copilot]

Pull request overview

This PR changes the library’s public API surface to export the main chain class as a named RspackChain export (instead of a default export), aligning runtime and type entrypoints and updating examples/tests accordingly.

Changes:

• Replace the default export with a named RspackChain export in the runtime entry (src/index.js).
• Update TypeScript declaration entrypoint to export RspackChain (class + merged namespace) instead of a default export.
• Update README, runtime tests, and type tests to use import { RspackChain } from 'rspack-chain'.

Reviewed changes

Copilot reviewed 4 out of 5 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
src/index.js	Renames main class to RspackChain and exports it as a named export.
types/index.d.ts	Switches public types from default export Config to named RspackChain and updates nested types accordingly.
types/test/rspack-chain-tests.ts	Updates type-level usage to RspackChain and adjusts related expectations.
test/Config.js	Updates runtime tests to import/instantiate RspackChain and use RspackChain.toString.
README.md	Updates documentation examples and headings from Config to RspackChain.

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