Feat add ttree merger

src/odapt/__init__.py

@@ -6,6 +6,9 @@
 from __future__ import annotations
 
 from odapt._version import __version__
-from odapt.operations import hadd  # noqa: F401
+from odapt.operations import (
+    hadd,  # noqa: F401
+    merge,  # noqa: F401
+)
 
 __all__ = ["__version__"]

src/odapt/operations/__init__.py

@@ -1,3 +1,4 @@
 from __future__ import annotations
 
-from odapt.operations.hadd import hadd, main  # noqa: F401
+from odapt.operations.hadd import hadd_1d, hadd_2d, hadd_3d  # noqa: F401
+from odapt.operations.merge import hadd_and_merge  # noqa: F401