Fix OCPNeb trainer loading (#995)

* add option to specify trainer for openneb; pass loss_functions to avoid breaking update_config

* fix test

src/fairchem/applications/cattsunami/core/ocpneb.py

@@ -36,6 +36,7 @@ def __init__(
         precon=None,
         cpu=False,
         batch_size=4,
+        trainer=None,
     ):
         """
         Subclass of NEB that allows for scaled and dynamic optimizations of
@@ -97,11 +98,14 @@ def __init__(
         if "relax_dataset" in config["task"]:
             del config["task"]["relax_dataset"]
 
-        self.trainer = registry.get_trainer_class(config.get("trainer", "ocp"))(
+        if trainer is None:
+            trainer = config.get("trainer", "ocp")
+
+        self.trainer = registry.get_trainer_class(trainer)(
             task=config.get("task", {}),
             model=config["model"],
             outputs={},
-            loss_functions={},
+            loss_functions=config.get("loss_functions", {}),
             evaluation_metrics={},
             dataset=[config["dataset"]],
             optimizer=config["optim"],