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)

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

codex-rs/exec-server/Cargo.toml

@@ -41,7 +41,8 @@ uuid = { workspace = true, features = ["v4"] }
 
 [dev-dependencies]
 anyhow = { workspace = true }
-codex-utils-cargo-bin = { workspace = true }
+codex-test-binary-support = { workspace = true }
+ctor = { workspace = true }
 pretty_assertions = { workspace = true }
 serial_test = { workspace = true }
 tempfile = { workspace = true }