Fix thread/list cwd filtering for Windows verbatim paths (#17414)

Addresses #17302

Problem: `thread/list` compared cwd filters with raw path equality, so
`resume --last` could miss Windows sessions when the saved cwd used a
verbatim path form and the current cwd did not.

Solution: Normalize cwd comparisons through the existing path comparison
utilities before falling back to direct equality, and add Windows
regression coverage for verbatim paths. I made this a general utility
function and replaced all of the duplicated instance of it across the
code base.

codex-rs/exec/src/lib.rs

@@ -1205,13 +1205,7 @@ async fn parse_latest_turn_context_cwd(path: &Path) -> Option<PathBuf> {
 }
 
 fn cwds_match(current_cwd: &Path, session_cwd: &Path) -> bool {
-    match (
-        path_utils::normalize_for_path_comparison(current_cwd),
-        path_utils::normalize_for_path_comparison(session_cwd),
-    ) {
-        (Ok(current), Ok(session)) => current == session,
-        _ => current_cwd == session_cwd,
-    }
+    path_utils::paths_match_after_normalization(current_cwd, session_cwd)
 }
 
 async fn resolve_resume_thread_id(