Bug: Despite being an optional peer dependency, the "features" package requires the "ssr" package

[TomStrepsil]

When trying to use the "features" package without also installing the "ssr" package, an error is thrown.

The "ssr" package is only needed when using the ssrBackedReactContextFeaturesStoreFactory

Due to monorepo package hoisting, this wasn't obvious in the "next" example that does not need the "ssr" package (since NextJs provides this facility through getServerSideProps etc)

To fix, may need to move to package exports, so that consumers can get a nuanced bundle containing only what they need.