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/core/src/models_manager/model_info.rs

@@ -10,8 +10,8 @@ use codex_protocol::openai_models::WebSearchToolType;
 use codex_protocol::openai_models::default_input_modalities;
 
 use crate::config::Config;
-use crate::features::Feature;
 use crate::truncate::approx_bytes_for_tokens;
+use codex_features::Feature;
 use tracing::warn;
 
 pub const BASE_INSTRUCTIONS: &str = include_str!("../../prompt.md");