feat(item_storage): implement item_storage_memory max_size

Implemented with unordered dict and set.

invokeai/app/services/item_storage/item_storage_memory.py

@@ -1,3 +1,4 @@
+from contextlib import suppress
 from typing import Generic, Optional, TypeVar
 
 from pydantic import BaseModel
@@ -8,21 +9,43 @@ T = TypeVar("T", bound=BaseModel)
 
 
 class ItemStorageMemory(ItemStorageABC, Generic[T]):
-    def __init__(self, id_field: str = "id") -> None:
+    """
+    Provides a simple in-memory storage for items, with a maximum number of items to store.
+    An item is deleted when the maximum number of items is reached and a new item is added.
+    There is no guarantee about which item will be deleted.
+    """
+
+    def __init__(self, id_field: str = "id", max_items: int = 10) -> None:
         super().__init__()
+        if max_items < 1:
+            raise ValueError("max_items must be at least 1")
+        if not id_field:
+            raise ValueError("id_field must not be empty")
         self._id_field = id_field
         self._items: dict[str, T] = {}
+        self._item_ids: set[str] = set()
+        self._max_items = max_items
 
     def get(self, item_id: str) -> Optional[T]:
         return self._items.get(item_id)
 
     def set(self, item: T) -> None:
-        self._items[getattr(item, self._id_field)] = item
+        item_id = getattr(item, self._id_field)
+        assert isinstance(item_id, str)
+        if item_id in self._items or len(self._items) < self._max_items:
+            # If the item is already stored, or we have room for more items, we can just add it.
+            self._items[item_id] = item
+            self._item_ids.add(item_id)
+        else:
+            # Otherwise, we need to make room for it first.
+            self._items.pop(self._item_ids.pop())
+            self._items[item_id] = item
+            self._item_ids.add(item_id)
         self._on_changed(item)
 
     def delete(self, item_id: str) -> None:
-        try:
+        # Both of these are no-ops if the item doesn't exist.
+        with suppress(KeyError):
             del self._items[item_id]
+            self._item_ids.remove(item_id)
             self._on_deleted(item_id)
-        except KeyError:
-            pass