ref: state - 2 (#4229)

Extracting tasks in a module and start abstraction behind a Trait (more
to come on this but each task will be tackled in a dedicated PR)
The goal was to drop the ActiveTask and to have a (potentially) set of
tasks during each turn

codex-rs/Cargo.lock

@@ -673,6 +673,7 @@ dependencies = [
  "askama",
  "assert_cmd",
  "async-channel",
+ "async-trait",
  "base64",
  "bytes",
  "chrono",
@@ -685,6 +686,7 @@ dependencies = [
  "env-flags",
  "eventsource-stream",
  "futures",
+ "indexmap 2.10.0",
  "landlock",
  "libc",
  "maplit",