[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/Cargo.toml

@@ -17,6 +17,7 @@ workspace = true
 codex-exec-server = { workspace = true }
 codex-login = { workspace = true }
 codex-utils-absolute-path = { workspace = true }
+codex-utils-path-uri = { workspace = true }
 serde = { workspace = true, features = ["derive"] }
 serde_json = { workspace = true }