Centralize turn environment selection state (#38461)

## What changed

- Store `TurnEnvironmentSelection` directly on each resolved `TurnEnvironment`
  instead of copying its environment ID, working directory, and workspace roots
  into separate fields.
- Update environment resolution, tool execution, approvals, and related tests to
  access selection state through the retained value.

GitOrigin-RevId: ab723d21e112b8af5bcaf1f772a5e376553312bc

codex-rs/core/src/context/world_state/environment.rs

@@ -342,7 +342,7 @@ fn environment_states(snapshot: &TurnEnvironmentSnapshot) -> BTreeMap<String, En
         .enumerate()
         .map(|(index, environment)| {
             (
-                environment.environment_id.clone(),
+                environment.selection.environment_id.clone(),
                 EnvironmentState {
                     cwd: environment.cwd().clone(),
                     status: EnvironmentStatus::Available,