chore: restore the debug package in the dev bundle

The debug package was not included anymore in the dev bundle since the
migration from webpack to rollup ([1]) in version 6.0.0.

[1]: https://github.com/socketio/engine.io-client/commit/27de300de42420ab59a02ec7a3445e636cbcc78e

See also: https://github.com/socketio/engine.io-client/commit/4683a954d4ac265d1ad75bc813d6bc4388ba7f37