added eval script and documentation

eval.py

@@ -0,0 +1,64 @@
+"""
+Usage:
+python eval.py --checkpoint data/image/pusht/diffusion_policy_cnn/train_0/checkpoints/latest.ckpt -o data/pusht_eval_output
+"""
+
+import sys
+# use line-buffering for both stdout and stderr
+sys.stdout = open(sys.stdout.fileno(), mode='w', buffering=1)
+sys.stderr = open(sys.stderr.fileno(), mode='w', buffering=1)
+
+import os
+import pathlib
+import click
+import hydra
+import torch
+import dill
+import wandb
+import json
+from diffusion_policy.workspace.base_workspace import BaseWorkspace
+
+@click.command()
+@click.option('-c', '--checkpoint', required=True)
+@click.option('-o', '--output_dir', required=True)
+@click.option('-d', '--device', default='cuda:0')
+def main(checkpoint, output_dir, device):
+    if os.path.exists(output_dir):
+        click.confirm(f"Output path {output_dir} already exists! Overwrite?", abort=True)
+    pathlib.Path(output_dir).mkdir(parents=True, exist_ok=True)
+    
+    # load checkpoint
+    payload = torch.load(open(checkpoint, 'rb'), pickle_module=dill)
+    cfg = payload['cfg']
+    cls = hydra.utils.get_class(cfg._target_)
+    workspace = cls(cfg, output_dir=output_dir)
+    workspace: BaseWorkspace
+    workspace.load_payload(payload, exclude_keys=None, include_keys=None)
+    
+    # get policy from workspace
+    policy = workspace.model
+    if cfg.training.use_ema:
+        policy = workspace.ema_model
+    
+    device = torch.device(device)
+    policy.to(device)
+    policy.eval()
+    
+    # run eval
+    env_runner = hydra.utils.instantiate(
+        cfg.task.env_runner,
+        output_dir=output_dir)
+    runner_log = env_runner.run(policy)
+    
+    # dump log to json
+    json_log = dict()
+    for key, value in runner_log.items():
+        if isinstance(value, wandb.sdk.data_types.video.Video):
+            json_log[key] = value._path
+        else:
+            json_log[key] = value
+    out_path = os.path.join(output_dir, 'eval_log.json')
+    json.dump(json_log, open(out_path, 'w'), indent=2, sort_keys=True)
+
+if __name__ == '__main__':
+    main()