refactor: move targets in Python SDK to sub module (#1028)

Author: georgeh0

python/cocoindex/targets/__init__.py

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

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

@@ -3,10 +3,10 @@
 from dataclasses import dataclass
 from typing import Sequence
 
-from . import op
-from . import index
-from .auth_registry import AuthEntryReference
-from .setting import DatabaseConnectionSpec
+from .. import op
+from .. import index
+from ..auth_registry import AuthEntryReference
+from ..setting import DatabaseConnectionSpec
 
 
 class Postgres(op.TargetSpec):