[codex] migrate ExecutorFileSystem paths to PathUri (#27424)

## Why

We're moving exec-server to use PathUri for its internal path
representations.

## What

Move `ExecutorFileSystem` APIs to use `PathUri` instead of
`AbsolutePathBuf`. Future changes will convert higher-level parts of
exec-server.

codex-rs/utils/plugins/src/plugin_namespace.rs

@@ -2,6 +2,7 @@
 
 use codex_exec_server::ExecutorFileSystem;
 use codex_utils_absolute_path::AbsolutePathBuf;
+use codex_utils_path_uri::PathUri;
 use std::path::Path;
 use std::path::PathBuf;
 
@@ -29,7 +30,8 @@ async fn plugin_manifest_name(
     let mut manifest_path = None;
     for relative_path in DISCOVERABLE_PLUGIN_MANIFEST_PATHS {
         let candidate = plugin_root.join(relative_path);
-        match fs.get_metadata(&candidate, /*sandbox*/ None).await {
+        let candidate_uri = PathUri::from_abs_path(&candidate).ok()?;
+        match fs.get_metadata(&candidate_uri, /*sandbox*/ None).await {
             Ok(metadata) if metadata.is_file => {
                 manifest_path = Some(candidate);
                 break;
@@ -38,8 +40,9 @@ async fn plugin_manifest_name(
         }
     }
     let manifest_path = manifest_path?;
+    let manifest_path_uri = PathUri::from_abs_path(&manifest_path).ok()?;
     let contents = fs
-        .read_file_text(&manifest_path, /*sandbox*/ None)
+        .read_file_text(&manifest_path_uri, /*sandbox*/ None)
         .await
         .ok()?;
     let RawPluginManifestName { name: raw_name } = serde_json::from_str(&contents).ok()?;