Introduce V2 of current and historical functions

wow_token/db/cached_range.py

@@ -0,0 +1,14 @@
+class CachedRange:
+    _PRECOMPUTE_RANGES = ['30d', '90d', '6m', '1y', '2y', 'all']
+    # I despise magic strings but this is about as good as I can get without enum support
+    def __init__(self, _range: str):
+        if _range not in CachedRange._PRECOMPUTE_RANGES:
+            raise ValueError(f'Invalid range: {_range}')
+        self._range = _range
+
+    @property
+    def range(self):
+        return self._range
+
+    def __str__(self):
+        return self._range