Enhance BaseDevice methods with detailed parsing documentation

- Updated the `vlans`, `interfaces`, and `system` methods in the `BaseDevice` class to include comprehensive docstrings outlining expected raw data structures and error handling.
- Modified the `Interfaces` model in `contract.py` to allow optional fields for `ip_address` and `mask`, improving flexibility in interface definitions.

oxi/interfaces/contract.py

@@ -3,8 +3,9 @@ from pydantic import BaseModel, Field
 
 
 class Interfaces(BaseModel):
-    ip_address: IPv4Address
-    mask: int
+    name: str
+    ip_address: IPv4Address | None = None
+    mask: int | None = None
     description: str