Implement example with rsky-firehose

The initial implementation of Rusty Statusphere uses [Rocketman](https://crates.io/crates/rocketman) to consume the Bluesky [Jetstream](https://docs.bsky.app/blog/jetstream).

It would be great to have an example that uses rsky's implementation of firehose as well that can be toggled via an env variable.

https://github.com/blacksky-algorithms/rsky/tree/main/rsky-firehose

Start with the existing Rusty Statusphere example's Rocketman consumer and the linked rsky-firehose implementation at rsky/rsky-firehose. Done means the example can select rsky-firehose or Rocketman through an environment variable while retaining the same statusphere behavior.

Written by the indexing model from the issue text.