core: add helper to 'freeze' dataclasses, in order to derive a schema from the properties

my/core/common.py

@@ -556,3 +556,9 @@ def to_jsons(it) -> Iterable[Json]:
 
 datetime_naive = datetime
 datetime_aware = datetime
+
+
+def assert_subpackage(name: str) -> None:
+    # can lead to some unexpected issues if you 'import cachew' which being in my/core directory.. so let's protect against it
+    # NOTE: if we use overlay, name can be smth like my.origg.my.core.cachew ...
+    assert 'my.core' in name, f'Expected module __name__ ({name}) to start with my.core'