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/mcp-server/src/message_processor.rs

@@ -7,6 +7,7 @@ use codex_core::config::Config;
 use codex_core::default_client::USER_AGENT_SUFFIX;
 use codex_core::default_client::get_codex_user_agent;
 use codex_core::models_manager::collaboration_mode_presets::CollaborationModesConfig;
+use codex_features::Feature;
 use codex_protocol::ThreadId;
 use codex_protocol::protocol::SessionSource;
 use codex_protocol::protocol::Submission;
@@ -65,7 +66,7 @@ impl MessageProcessor {
             CollaborationModesConfig {
                 default_mode_request_user_input: config
                     .features
-                    .enabled(codex_core::features::Feature::DefaultModeRequestUserInput),
+                    .enabled(Feature::DefaultModeRequestUserInput),
             },
         ));
         Self {