fix: Don't cache anything hashable

If filters are list or dict then they aren't hashable, there was little
reason to do this IMO.

If something is indeed cacheable then where is the eviction for it?
simple k:v is only thing we can realistically cache here.

frappe/database/database.py

@@ -595,7 +595,7 @@ class Database:
 		"""
 		out = None
 		cache_key = None
-		if cache and isinstance(filters, Hashable):
+		if cache and isinstance(filters, str):
 			cache_key = (doctype, filters, fieldname)
 			if cache_key in self.value_cache:
 				return self.value_cache[cache_key]