Redirect to http resources by default

[pelson]

#15 relates.

This introduces a binary flag on the router to allow you to toggle between streaming and redirect. Streaming makes sense when you are in an air-gapped environment (the original motivator), or when the server has authentication credentials which the client might not (e.g. simple-repository/simple-repository#35). Redirect makes sense when you are using simple-repository-server to handle repository merging (e.g. of public repositories), it would also make pip/uv cache more efficient (tested: pip shows that it is caching the non-redirected URL, but it actually caches the final URL) as the terminal URL will reach pip/uv and can be pooled with other requests to the same location (that don't go through simple-repository-server.

In the future, I hope that #15 will address the ability to get_resource of a byte-stream (irrespective of source), allowing unknown protocols to work seamlessly. In that scenario, I hope the that the stream doesn't start until requested, and that there will be enough context to know that for http resources we might return a redirect response instead. In that world, it would be a component-level behaviour whether streaming is forced or not - if you want to disable redirecting, you simply hide the source URL in your get_resource response and the server can do nothing other than streaming. There, this flag would continue to make sense, but would be something we can move down into a component (and eventually remove from the build_router function.