Wire with_remote_overrides to construct model families (#7621)

- This PR wires `with_remote_overrides` and make the
`construct_model_families` an async function
- Moves getting model family a level above to keep the function `sync`
- Updates the tests to local, offline, and `sync` helper for model
families

codex-rs/core/Cargo.toml

@@ -90,6 +90,7 @@ wildmatch = { workspace = true }
 
 [features]
 deterministic_process_ids = []
+test-support = []
 
 
 [target.'cfg(target_os = "linux")'.dependencies]