Third-party reference code

Reference repositories are inspected here but are not vendored into this project. They are not runtime dependencies.

The track-GRU design was checked against the official EgoSpeak repository at revision b5bee35e796d8f2d6aa7da2bf1b07836270f8bfb:

git clone https://github.com/jun297/EgoSpeak.git third_party/EgoSpeak
git -C third_party/EgoSpeak checkout b5bee35e796d8f2d6aa7da2bf1b07836270f8bfb

third_party/EgoSpeak/ is intentionally ignored. No EgoSpeak source file is copied or imported by the project implementation.