Resolve ReadableStream types for `getPlatformProxy()`

```suggestion
// @ts-expect-error `ReadableStream` between Node.js and Workers doesn't quite along (Property 'readAtLeast' is missing in type 'import("stream/web").ReadableStreamBYOBReader')
```

This method is [non-standard](https://developers.cloudflare.com/workers/runtime-apis/streams/readablestreambyobreader/#:~:text=readAtLeast%20is%20a%20non%2Dstandard%20extension%20to%20the%20Streams%20API%20which%20allows%20users%20to%20specify%20that%20at%20least%20minBytes%20bytes%20must%20be%20read%20into%20the%20buffer%20before%20resolving%20the%20read.)

What happens if the IMAGE binding actually starts to use this?

Should we have some kind of transform/polyfill for `getPlatformProxy()`?

_Originally posted by @petebacondarwin in https://github.com/cloudflare/workers-sdk/pull/9954#discussion_r2207446897_

Start from the getPlatformProxy() implementation and the suggested @ts-expect-error, then compare the Node.js stream/web and Workers ReadableStream types. Check how the IMAGE binding could use readAtLeast; done means the compatibility approach is defined and the resulting types work without masking the mismatch.

Written by the indexing model from the issue text.