chore: rework tools execution workflow (#5278)

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

codex-rs/core/src/lib.rs

@@ -25,9 +25,7 @@ pub mod custom_prompts;
 mod environment_context;
 pub mod error;
 pub mod exec;
-mod exec_command;
 pub mod exec_env;
-pub mod executor;
 pub mod features;
 mod flags;
 pub mod git_info;
@@ -38,6 +36,7 @@ mod mcp_tool_call;
 mod message_history;
 mod model_provider_info;
 pub mod parse_command;
+pub mod sandboxing;
 pub mod token_data;
 mod truncate;
 mod unified_exec;
@@ -59,7 +58,6 @@ pub use auth::CodexAuth;
 pub mod default_client;
 pub mod model_family;
 mod openai_model_info;
-mod openai_tools;
 pub mod project_doc;
 mod rollout;
 pub(crate) mod safety;