Runs after tree-shaking

Thanks for amazing plugin.

I just found strange behavior, but don’t have experience to reproduce in other build.

In [our project](https://github.com/hplush/slowreader/), the plugin doesn’t affect JS bundle size (but change source code) until I [change calling order](https://github.com/hplush/slowreader/commit/9b4cbadafa691e93b8e704e939b537ceceb52986):

```diff
return {
+ enforce: 'pre',
name: 'rollup-plugin-pure',
transform: {
- order: 'post',
+ order: 'pre',
```

Seems like on some systems plugins runs before Vite/Rollup does static analysis for tree-shaking.

Here is our [Vite config](https://github.com/hplush/slowreader/blob/9b4cbadafa691e93b8e704e939b537ceceb52986/web/vite.config.ts).