Remove version_file setting and migrate to lazy version loading

Remove setuptools-scm version_file setting and replace static version import
with lazy loading via __getattr__ using importlib.metadata.version.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <[email protected]>

Author: RonnyPfannschmidt

changelog/590.trivial.rst

@@ -0,0 +1 @@
+Migrate from generating a version file to lazy loading it via importlib.

pyproject.toml

@@ -66,7 +66,6 @@ known-local-folder = ["pluggy"]
 lines-after-imports = 2
 
 [tool.setuptools_scm]
-version_file = "src/pluggy/_version.py"
 
 [tool.towncrier]
 package = "pluggy"

src/pluggy/__init__.py

@@ -25,6 +25,14 @@
 from ._manager import PluginValidationError
 from ._result import HookCallError
 from ._result import Result
-from ._version import version as __version__
 from ._warnings import PluggyTeardownRaisedWarning
 from ._warnings import PluggyWarning
+
+
+def __getattr__(name: str) -> str:
+    if name == "__version__":
+        from importlib.metadata import version
+
+        return version("pluggy")
+
+    raise AttributeError(f"module {__name__} has no attribute {name!r}")