Add support for local files and optimized caching

Signed-off-by: Felipe Cardoso <felipe.cardoso@hotmail.it>

backend/app/models/sample.py

@@ -1,5 +1,4 @@
 from datetime import datetime
-from typing import Optional
 
 from pydantic import BaseModel
 
@@ -8,4 +7,6 @@ class Sample(BaseModel):
     filename: str
     url: str
     created_at: datetime
-    step: Optional[int] = None
+    source: str  # 'local' or 'remote'
+    source_path: str  # full path to the file
+    size: int