Consider making BlobRef use interface instead of class

[mikuhl-dev]

BlobRef seems to be the only thing that uses a class, and this single object is preventing it from being serialized by Qwik

[devinivy]

The purpose of BlobRef is to help developers handle edge-cases around a legacy blob format (there's a legacy and a revised/final format for blobs), so I don't think this would be a trivial change. I don't know exactly how you're using this with qwik, but perhaps you could use the "plain json" version of these values, which can be generated by passing them through lexToJson from the @atproto/lexicon package.