REFACTOR: Refactor langchain_core (#13627)

Changes:
- remove langchain_core/schema since no clear distinction b/n schema and
non-schema modules
- make every module that doesn't end in -y plural
- where easy have 1-2 classes per file
- no more than one level of nesting in directories
- only import from top level core modules in langchain

libs/core/tests/unit_tests/utils/test_imports.py

@@ -14,6 +14,7 @@ EXPECTED_ALL = [
     "print_text",
     "raise_for_status_with_text",
     "xor_args",
+    "try_load_from_hub",
 ]