sources moved to sources subpackage in python sdk (cocoindex-io#1081)

Author: Davda-James

python/cocoindex/sources/__init__.py

@@ -0,0 +1,5 @@
+"""
+Sources supported by CocoIndex.
+"""
+
+from ._engine_builtin_specs import *

python/cocoindex/sources.py renamed to python/cocoindex/sources/_engine_builtin_specs.py

@@ -1,8 +1,8 @@
 """All builtin sources."""
 
-from . import op
-from .auth_registry import TransientAuthEntryReference
-from .setting import DatabaseConnectionSpec
+from .. import op
+from ..auth_registry import TransientAuthEntryReference
+from ..setting import DatabaseConnectionSpec
 from dataclasses import dataclass
 import datetime