feat: add __version__ attribute to package

Expose version attribute using importlib.metadata with pyproject.toml as single source of truth. Add unit tests to verify version attribute.

Author: brandonhawi

src/nba_api/__init__.py

@@ -1 +1,4 @@
+from importlib.metadata import version
+
 name = "nba_api"
+__version__ = version("nba_api")

tests/unit/test_version.py

@@ -0,0 +1,18 @@
+import nba_api
+from importlib.metadata import version
+
+
+def test_version_exists():
+    assert hasattr(nba_api, '__version__')
+
+
+def test_version_format():
+    assert isinstance(nba_api.__version__, str)
+    parts = nba_api.__version__.split('.')
+    assert len(parts) >= 2
+    for part in parts:
+        assert part.isdigit()
+
+
+def test_version_matches_metadata():
+    assert nba_api.__version__ == version("nba_api")