Add a native BRP HTTP client behind a client feature

[jbuehler23]

Objective

Part of #23013.

Add an async BRP client to bevy_remote so tools can call a running app from rust without blocking. This will be used by the inspector and in the future the editor.

Related to #20189 and #25818.

Solution

An async client behind an off by default client feature, on the same hyper and smol stack as the server, so no new dependencies. Calls run on bevy's io task pool and can be awaited or spawned from systems. Native only, like the http feature.

• call a method with optional params and get the result or a typed error (io, http, json, or the remote's own BRP error)
• a spawn variant that returns a task for use from systems
• a bevy_remote_client passthrough on the bevy crate so examples can ask for it

The integration test example uses it for instant calls. Watching methods are not covered yet since they are a server sent event stream.

AI disclosure

AI assistance was used to help port these changes and to plan this upstream series from our existing Jackdaw functionality. All changes were reviewed by a human before submission.