feat!: make package pure ESM

[chenjiahan]

This PR makes @rspack/plugin-preact-refresh a pure ESM package. It removes the CommonJS wrapper, main, and exports.require, switches Rslib to ESM-only output with ES2023 syntax, and exposes the root package through the default condition.

The README now shows ESM config usage, and the test fixtures read the ESM default export from the built package under Node 24.

[Copilot]

Pull request overview

This PR converts @rspack/plugin-preact-refresh into a pure ESM package by removing the CommonJS entrypoint/exports, switching the build output to ESM-only, and updating docs/tests to consume the plugin via ESM default export semantics.

Changes:

• Remove the CommonJS wrapper (index.cjs) and drop exports.require from package.json.
• Configure Rslib to emit only ESM + DTS outputs.
• Update README and test fixtures to use ESM-style default export consumption.

Reviewed changes

Copilot reviewed 16 out of 16 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
test/hotCases/with-worker/basic/rspack.config.js	Update fixture to read the plugin as an ESM default export via require() interop.
test/hotCases/jsx/with-same-name-component/rspack.config.js	Update fixture to read the plugin as an ESM default export via require() interop.
test/hotCases/jsx/value/rspack.config.js	Update fixture to read the plugin as an ESM default export via require() interop.
test/hotCases/jsx/child/rspack.config.js	Update fixture to read the plugin as an ESM default export via require() interop.
test/hotCases/jsx/basic/rspack.config.js	Update fixture to read the plugin as an ESM default export via require() interop.
test/hotCases/hook/useState_reset/rspack.config.js	Update fixture to read the plugin as an ESM default export via require() interop.
test/hotCases/hook/useState_keep/rspack.config.js	Update fixture to read the plugin as an ESM default export via require() interop.
test/hotCases/hook/useContext_provide/rspack.config.js	Update fixture to read the plugin as an ESM default export via require() interop.
test/hotCases/hook/useContext_keep/rspack.config.js	Update fixture to read the plugin as an ESM default export via require() interop.
test/hotCases/hook/useContext_initial/rspack.config.js	Update fixture to read the plugin as an ESM default export via require() interop.
test/configCases/condition/include/rspack.config.js	Update fixture import pattern and adjust plugins formatting.
test/configCases/condition/exclude/rspack.config.js	Update fixture import pattern and adjust plugins formatting.
rslib.config.ts	Switch library build output to ESM-only (with DTS).
README.md	Update usage examples to ESM import/export style and ESM-friendly require.resolve via createRequire.
package.json	Make the package pure ESM by removing CJS entrypoints/exports and updating main/exports/files.
index.cjs	Remove CommonJS compatibility entrypoint.

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