Stabilize exec-server filesystem tests in CI (#17671)

## Summary\n- add an exec-server package-local test helper binary that
can run exec-server and fs-helper flows\n- route exec-server filesystem
tests through that helper instead of cross-crate codex helper
binaries\n- stop relying on Bazel-only extra binary wiring for these
tests\n\n## Testing\n- not run (per repo guidance for codex changes)

---------

Co-authored-by: Codex <noreply@openai.com>

codex-rs/Cargo.toml

@@ -86,6 +86,7 @@ members = [
     "codex-api",
     "state",
     "terminal-detection",
+    "test-binary-support",
     "codex-experimental-api-macros",
     "plugin",
 ]
@@ -163,6 +164,7 @@ codex-skills = { path = "skills" }
 codex-state = { path = "state" }
 codex-stdio-to-uds = { path = "stdio-to-uds" }
 codex-terminal-detection = { path = "terminal-detection" }
+codex-test-binary-support = { path = "test-binary-support" }
 codex-tools = { path = "tools" }
 codex-tui = { path = "tui" }
 codex-utils-absolute-path = { path = "utils/absolute-path" }