refactor!: frappe.db.get_singles_dict

* Cast single's values as their fieldtypes before returning
* Support previously dead debug parameter
* Consider single with no meta as non-existent; skip query

Decided to go ahead with the breaking change given the nature of the
existing usages of get_singles_dict :crie:

frappe/database/database.py

@@ -1,4 +1,4 @@
-# Copyright (c) 2015, Frappe Technologies Pvt. Ltd. and Contributors
+# Copyright (c) 2022, Frappe Technologies Pvt. Ltd. and Contributors
 # License: MIT. See LICENSE
 
 # Database Module
@@ -18,6 +18,7 @@ import frappe
 import frappe.defaults
 import frappe.model.meta
 from frappe import _
+from frappe.exceptions import DoesNotExistError
 from frappe.model.utils.link_count import flush_local_link_count
 from frappe.query_builder.functions import Count
 from frappe.query_builder.utils import DocType
@@ -628,14 +629,28 @@ class Database(object):
 		        # Get coulmn and value of the single doctype Accounts Settings
 		        account_settings = frappe.db.get_singles_dict("Accounts Settings")
 		"""
-		result = self.query.get_sql(
+		return_value = frappe._dict()
+
+		try:
+			meta = frappe.get_meta(doctype)
+		except DoesNotExistError:
+			return return_value
+
+		queried_result = self.query.get_sql(
 			"Singles",
 			filters={"doctype": doctype},
 			fields=["field", "value"],
 			for_update=for_update,
-		).run()
+		).run(debug=debug)
 
-		return frappe._dict(result)
+		for fieldname, value in queried_result:
+			if df := meta.get_field(fieldname):
+				casted_value = cast(df.fieldtype, value)
+			else:
+				casted_value = value
+			return_value[fieldname] = casted_value
+
+		return return_value
 
 	@staticmethod
 	def get_all(*args, **kwargs):