make typing behavior of AgentSet.get explicit (projectmesa#2293)

* make typing behavior of AgentSet.get explicit

* [pre-commit.ci] auto fixes from pre-commit.com hooks

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---------

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

mesa/agent.py

@@ -20,7 +20,7 @@
 from random import Random
 
 # mypy
-from typing import TYPE_CHECKING, Any, Literal
+from typing import TYPE_CHECKING, Any, Literal, overload
 
 if TYPE_CHECKING:
     # We ensure that these are not imported during runtime to prevent cyclic
@@ -348,12 +348,28 @@ def agg(self, attribute: str, func: Callable) -> Any:
         values = self.get(attribute)
         return func(values)
 
+    @overload
     def get(
         self,
-        attr_names: str | list[str],
+        attr_names: str,
         handle_missing: Literal["error", "default"] = "error",
         default_value: Any = None,
-    ) -> list[Any] | list[list[Any]]:
+    ) -> list[Any]: ...
+
+    @overload
+    def get(
+        self,
+        attr_names: list[str],
+        handle_missing: Literal["error", "default"] = "error",
+        default_value: Any = None,
+    ) -> list[list[Any]]: ...
+
+    def get(
+        self,
+        attr_names,
+        handle_missing="error",
+        default_value=None,
+    ):
         """
         Retrieve the specified attribute(s) from each agent in the AgentSet.