refactor: make importlib metadata package import lazy

No reason I can discern for it, just a matter of traditions I guess.
#2405 (comment)

Author: dvarrazzo

isort/settings.py

@@ -45,12 +45,12 @@
 from .wrap_modes import WrapModes
 from .wrap_modes import from_string as wrap_mode_from_string
 
-if sys.version_info < (3, 10):  # pragma: no cover
-    from importlib_metadata import entry_points
-else:
-    from importlib.metadata import entry_points
-
 if TYPE_CHECKING:
+    if sys.version_info < (3, 10):  # pragma: no cover
+        EntryPoints = Any
+    else:
+        from importlib.metadata import EntryPoints
+
     tomllib: Any
 else:
     if sys.version_info >= (3, 11):
@@ -937,4 +937,17 @@ def _as_bool(value: str) -> bool:
         raise ValueError(f"invalid truth value {value}")
 
 
+def entry_points(group: str) -> "EntryPoints":
+    """Call entry_point after lazy loading it.
+
+    TODO: The reason for lazy loading here are unknown.
+    """
+    if sys.version_info < (3, 10):  # pragma: no cover
+        from importlib_metadata import entry_points
+    else:
+        from importlib.metadata import entry_points
+
+    return entry_points(group=group)
+
+
 DEFAULT_CONFIG = Config()

pyproject.toml

@@ -180,6 +180,10 @@ allow_untyped_defs = true
 allow_incomplete_defs = true
 allow_untyped_calls = true
 
+[[tool.mypy.overrides]]
+module = "importlib_metadata.*"
+ignore_missing_imports = true
+
 [tool.ruff]
 line-length = 100
 lint.select = [