refactor: move __version__ and __version_info__ into _version.py

Extract the version definitions from brainpy/__init__.py into a dedicated
brainpy/_version.py module and re-export them from the package root, so the
canonical version string lives in a single small file. pyproject already
reads brainpy.__version__ and lists _version.py in its coverage omit lists.

Author: chaoming0625

brainpy/__init__.py

@@ -14,8 +14,8 @@
 # limitations under the License.
 # ==============================================================================
 
-__version__ = "2.8.0"
-__version_info__ = tuple(map(int, __version__.split(".")))
+from brainpy._version import __version__ as __version__
+from brainpy._version import __version_info__ as __version_info__
 
 from brainpy import _errors as errors
 # fundamental supporting modules

brainpy/_version.py

@@ -0,0 +1,18 @@
+# -*- coding: utf-8 -*-
+# Copyright 2025 BrainX Ecosystem Limited. All Rights Reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+# ==============================================================================
+
+__version__ = "2.8.0"
+__version_info__ = tuple(map(int, __version__.split(".")))