chore: rework tools execution workflow (#5278)

Re-work the tool execution flow. Read `orchestrator.rs` to understand
the structure

codex-rs/core/src/chat_completions.rs

@@ -11,7 +11,7 @@ use crate::error::Result;
 use crate::error::RetryLimitReachedError;
 use crate::error::UnexpectedResponseError;
 use crate::model_family::ModelFamily;
-use crate::openai_tools::create_tools_json_for_chat_completions_api;
+use crate::tools::spec::create_tools_json_for_chat_completions_api;
 use crate::util::backoff;
 use bytes::Bytes;
 use codex_otel::otel_event_manager::OtelEventManager;