Rust dependency update triggers result_large_err in response helpers #17

@amccabe I looked into the Rust check failing on #12 and opened #16 with a small fix.

The Actix dependency update nudges the in-memory size of HttpResponse up to at least 128 bytes. Clippy then rejects the error variants returned by client() and check_auth() under -D warnings (result_large_err). This concerns the Rust object size, not the HTTP payload.

The proposed fix boxes those helper error responses and unwraps them at the handler boundaries, preserving the status codes and JSON bodies. Existing handler tests now assert the complete authentication and disconnected-database error bodies.

Validation passed with both main's lockfile and #12's lockfile at 51ae797a3c147aebe18c93ed0eea1dad48978896: formatting, Clippy with warnings denied, and all six Rust tests.

Failing upstream run: https://github.com/endgrainlabs/example-stack/actions/runs/35389695485/job/105744895037

Proposed fix: #16.