[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/git-utils/Cargo.toml

@@ -14,6 +14,7 @@ chrono = { workspace = true }
 codex-file-system = { workspace = true }
 codex-protocol = { workspace = true }
 codex-utils-absolute-path = { workspace = true }
+codex-utils-path-uri = { workspace = true }
 futures = { workspace = true, features = ["alloc"] }
 gix = { workspace = true }
 once_cell = { workspace = true }