This PR replaces our $state wrapper around the passed in props with a custom $state.raw + Proxy solution to create a "shallow state" around props

This shallow state allows rerender to continue to function while avoiding the weirdness of implicitly turning everything inside props into a Proxy, which is not how Svelte operates at runtime.

Long term, we should probably remove rerender and any internal reactive state entirely. If a user needs to rerender, they can pass their own $state in themselves. Happily, this new implementation already supports that, so I can explore a deprecation notice and update to the docs in a follow-up

Fixes #455