chore: move dependencies, add more tests

src/bibapi/schemas/errors.py

@@ -0,0 +1,10 @@
+class BibAPIError(Exception):
+    """Base class for all BibAPI errors."""
+
+
+class CatalogueError(BibAPIError):
+    """Raised when there is an error with the library catalogue API."""
+
+
+class NetworkError(BibAPIError):
+    """Raised when there is a network-related error."""