Add Image models and clean up test code structure

Introduced `ImageCreate` and `Image` models to handle image-related data in the backend. Improved the organization and readability of the testing notebook by consolidating and formatting code into distinct sections with markdown cells.

backend/app/schemas.py

@@ -783,3 +783,24 @@ class Beamtime(BaseModel):
     proposal: Optional[Proposal]
     local_contact_id: Optional[int]
     local_contact: Optional[LocalContact]
+
+    class Config:
+        from_attributes = True
+
+
+class ImageCreate(BaseModel):
+    pgroup: str
+    sample_id: int
+    filepath: str
+    status: str = "active"
+    comment: Optional[str] = None
+
+    class Config:
+        from_attributes = True
+
+
+class Image(ImageCreate):
+    id: int
+
+    class Config:
+        from_attributes = True