Refactor gnn training (#252) * minor upds * refactor: training pipeline * feat: find gcs image path * feat: feature generation in trainer * feat: validation sets in training * bug: hgraph forward passes with missing edge types * refactor: hgnn trainer * feat: functional training pipeline * bug: set validation data * refactor: combined train engine and pipeline * refactor: infernce pipeline, evaluation --------- Co-authored-by: anna-grim <[email protected]>