Implement backend API for landmarks, trip optimization, and toilet locations

- Added landmarks_router.py to handle landmark retrieval based on user preferences and location.
- Implemented optimization_router.py for trip optimization, including handling preferences and landmarks.
- Created toilets_router.py to fetch toilet locations within a specified radius from a given location.
- Enhanced error handling and logging across all new endpoints.
- Generated a comprehensive report.html for test results and environment details.

backend/src/structs/preferences.py

@@ -1,7 +1,7 @@
 """Defines the Preferences used as input for trip generation."""
 
 from typing import Optional, Literal
-from pydantic import BaseModel
+from pydantic import BaseModel, field_validator
 
 
 class Preference(BaseModel) :
@@ -15,6 +15,13 @@ class Preference(BaseModel) :
     type: Literal['sightseeing', 'nature', 'shopping', 'start', 'finish']
     score: int          # score could be from 1 to 5
 
+    @field_validator("type")
+    @classmethod
+    def validate_type(cls, v):
+        if v not in {'sightseeing', 'nature', 'shopping', 'start', 'finish'}:
+            raise ValueError(f"Invalid type: {v}")
+        return v
+
 
 # Input for optimization
 class Preferences(BaseModel) :