[booster] make optimizer argument optional for boost (#3993)

* feat: make optimizer optional in Booster.boost

* test: skip unet test if diffusers version > 0.10.2

tests/test_autochunk/test_autochunk_diffuser/test_autochunk_unet.py

@@ -4,12 +4,15 @@ import pytest
 import torch
 
 try:
-    from diffusers import UNet2DModel
-    MODELS = [UNet2DModel]
+    import diffusers
+    MODELS = [diffusers.UNet2DModel]
     HAS_REPO = True
+    from packaging import version
+    SKIP_UNET_TEST = version.parse(diffusers.__version__) > version.parse("0.10.2")
 except:
     MODELS = []
     HAS_REPO = False
+    SKIP_UNET_TEST = False
 
 from test_autochunk_diffuser_utils import run_test
 
@@ -32,6 +35,10 @@ def get_data(shape: tuple) -> Tuple[List, List]:
     return meta_args, concrete_args
 
 
+@pytest.mark.skipif(
+    SKIP_UNET_TEST,
+    reason="diffusers version > 0.10.2",
+)
 @pytest.mark.skipif(
     not (AUTOCHUNK_AVAILABLE and HAS_REPO),
     reason="torch version is lower than 1.12.0",