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/tests/common/Cargo.toml

@@ -11,7 +11,7 @@ path = "lib.rs"
 anyhow = { workspace = true }
 assert_cmd = { workspace = true }
 base64 = { workspace = true }
-codex-core = { workspace = true }
+codex-core = { workspace = true, features = ["test-support"] }
 codex-protocol = { workspace = true }
 notify = { workspace = true }
 regex-lite = { workspace = true }