Range requests for cache API

[cceckman-at-fastly]

Support range requests in the cache API.

This completes options processing for the "lookup" side, so remove the EXPERIMENTAL flag for those calls. The insert side doesn't handle all the options, though, so it's still required for a complete workflow.

[cceckman-at-fastly]

@aturon and I discussed this today. While this accurately represents what Compute Platform does... this is a bad behavior and we don't want to support it.

We have a strategy to roll out a fix that gives the sensible behavior for to_stream_from_range. I'm going to switch this back to a draft, and will eventually republish it with the revised behavior.