Scheduler type annotations (#9030)

* Reduce dask.order overhead by removing stripped_dep computation

* Finish scheduler type annotations

* fix tests

Author: fjetter

distributed/client.py

@@ -886,7 +886,7 @@ def keys(self) -> Iterable[Key]:
     def _meta(self):
         return []
 
-    def _layer(self):
+    def _layer(self) -> dict[Key, GraphNode]:
         dsk: _T_LowLevelGraph = {}
 
         if not self.kwargs:

distributed/preloading.py

@@ -251,8 +251,8 @@ def __len__(self) -> int:
 
 def process_preloads(
     dask_server: Server | Client,
-    preload: str | list[str],
-    preload_argv: list[str] | list[list[str]],
+    preload: str | Sequence[str],
+    preload_argv: Sequence[str] | Sequence[Sequence[str]],
     *,
     file_dir: str | None = None,
 ) -> PreloadManager: