Added singleton config and changed module structure

neuroapi/config.py

@@ -0,0 +1,19 @@
+import os
+from typing import Self
+
+from dotenv import load_dotenv
+
+
+class _Singleton:
+    _instances = {}
+    
+    def __new__(cls) -> Self:
+        if cls not in cls._instances:
+            cls._instances[cls] = super(_Singleton, cls).__new__(cls)
+        return cls._instances[cls]
+
+class Config(_Singleton):
+    api_url: str
+    def __init__(self):
+        load_dotenv(os.path.join(os.path.dirname(__file__), '..', '.env'))
+        self.api_url = os.environ.get('API_URL')