feat(nodes): allow _delete_all in obj serializer to be called at any time

`_delete_all` logged how many items it deleted, and had to be called _after_ service start bc it needed access to logger.

Move the logger call to the startup method and return the the deleted stats from `_delete_all`. This lets `_delete_all` be called at any time.

invokeai/app/services/object_serializer/object_serializer_ephemeral_disk.py

@@ -1,4 +1,5 @@
 import typing
+from dataclasses import dataclass
 from pathlib import Path
 from typing import Optional, TypeVar
 
@@ -12,6 +13,12 @@ from invokeai.app.util.misc import uuid_string
 T = TypeVar("T")
 
 
+@dataclass
+class DeleteAllResult:
+    deleted_count: int
+    freed_space_bytes: float
+
+
 class ObjectSerializerEphemeralDisk(ObjectSerializerBase[T]):
     """Provides a disk-backed ephemeral storage for arbitrary python objects. The storage is cleared at startup.
 
@@ -26,7 +33,12 @@ class ObjectSerializerEphemeralDisk(ObjectSerializerBase[T]):
 
     def start(self, invoker: Invoker) -> None:
         self._invoker = invoker
-        self._delete_all()
+        delete_all_result = self._delete_all()
+        if delete_all_result.deleted_count > 0:
+            freed_space_in_mb = round(delete_all_result.freed_space_bytes / 1024 / 1024, 2)
+            self._invoker.services.logger.info(
+                f"Deleted {delete_all_result.deleted_count} {self._obj_class_name} files (freed {freed_space_in_mb}MB)"
+            )
 
     def load(self, name: str) -> T:
         file_path = self._get_path(name)
@@ -58,18 +70,14 @@ class ObjectSerializerEphemeralDisk(ObjectSerializerBase[T]):
     def _new_name(self) -> str:
         return f"{self._obj_class_name}_{uuid_string()}"
 
-    def _delete_all(self) -> None:
+    def _delete_all(self) -> DeleteAllResult:
         """
         Deletes all objects from disk.
-        Must be called after we have access to `self._invoker` (e.g. in `start()`).
         """
 
         # We could try using a temporary directory here, but they aren't cleared in the event of a crash, so we'd have
         # to manually clear them on startup anyways. This is a bit simpler and more reliable.
 
-        if not self._invoker:
-            raise ValueError("Invoker is not set. Must call `start()` first.")
-
         deleted_count = 0
         freed_space = 0
         for file in Path(self._output_dir).glob("*"):
@@ -77,8 +85,4 @@ class ObjectSerializerEphemeralDisk(ObjectSerializerBase[T]):
                 freed_space += file.stat().st_size
                 deleted_count += 1
                 file.unlink()
-        if deleted_count > 0:
-            freed_space_in_mb = round(freed_space / 1024 / 1024, 2)
-            self._invoker.services.logger.info(
-                f"Deleted {deleted_count} {self._obj_class_name} files (freed {freed_space_in_mb}MB)"
-            )
+        return DeleteAllResult(deleted_count, freed_space)