Split features into codex-features crate (#15253)

- Split the feature system into a new `codex-features` crate.
- Cut `codex-core` and workspace consumers over to the new config and
warning APIs.

Co-authored-by: Ahmed Ibrahim <219906144+aibrahim-oai@users.noreply.github.com>
Co-authored-by: Codex <noreply@openai.com>

codex-rs/app-server-client/src/lib.rs

@@ -47,6 +47,7 @@ use codex_core::config::Config;
 use codex_core::config_loader::CloudRequirementsLoader;
 use codex_core::config_loader::LoaderOverrides;
 use codex_core::models_manager::collaboration_mode_presets::CollaborationModesConfig;
+use codex_features::Feature;
 use codex_feedback::CodexFeedback;
 use codex_protocol::protocol::SessionSource;
 use serde::de::DeserializeOwned;
@@ -215,7 +216,7 @@ impl InProcessClientStartArgs {
                 default_mode_request_user_input: self
                     .config
                     .features
-                    .enabled(codex_core::features::Feature::DefaultModeRequestUserInput),
+                    .enabled(Feature::DefaultModeRequestUserInput),
             },
         ));
 
@@ -1484,7 +1485,7 @@ mod tests {
             CollaborationModesConfig {
                 default_mode_request_user_input: config
                     .features
-                    .enabled(codex_core::features::Feature::DefaultModeRequestUserInput),
+                    .enabled(Feature::DefaultModeRequestUserInput),
             },
         ));
         event_tx