[Core] Document all exported core methods with type hints

Standardize docstrings in core.py to google standard.
Remove type hints in docstrings in favor of the ones in method signatures.

Use function signature type hints in autodoc generated docs.

Closes: https://github.com/deluge-torrent/deluge/pull/359

docs/source/conf.py

@@ -48,6 +48,7 @@ extensions = [
     'sphinx.ext.coverage',
     'sphinxcontrib.spelling',
     'myst_parser',
+    'sphinx_autodoc_typehints',
 ]
 
 napoleon_include_init_with_doc = True