refactor: route market providers through data gateway

backend/data/contracts.py

@@ -0,0 +1,29 @@
+from __future__ import annotations
+
+from dataclasses import dataclass
+from typing import Literal
+
+
+DataUsage = Literal["display", "calculation"]
+
+
+@dataclass(frozen=True)
+class ProviderContract:
+    id: str
+    provider_class: str
+    calculation_allowed: bool
+
+
+@dataclass(frozen=True)
+class DatasetContract:
+    id: str
+    entity: str
+    frequency: str
+    primary: str
+    fallbacks: tuple[str, ...]
+    usage: str
+    fields: tuple[str, ...]
+
+    @property
+    def providers(self) -> tuple[str, ...]:
+        return (self.primary, *self.fallbacks)