feat(item_storage): implement item_storage_memory with LRU eviction strategy

Implemented with OrderedDict.

invokeai/app/services/item_storage/item_storage_memory.py

@@ -1,3 +1,4 @@
+from collections import OrderedDict
 from contextlib import suppress
 from typing import Generic, Optional, TypeVar
 
@@ -11,8 +12,7 @@ T = TypeVar("T", bound=BaseModel)
 class ItemStorageMemory(ItemStorageABC, Generic[T]):
     """
     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.
+    The storage uses the LRU strategy to evict items from storage when the max has been reached.
     """
 
     def __init__(self, id_field: str = "id", max_items: int = 10) -> None:
@@ -22,30 +22,29 @@ class ItemStorageMemory(ItemStorageABC, Generic[T]):
         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._items: OrderedDict[str, T] = OrderedDict()
         self._max_items = max_items
 
     def get(self, item_id: str) -> Optional[T]:
+        # If the item exists, move it to the end of the OrderedDict.
+        item = self._items.pop(item_id, None)
+        if item is not None:
+            self._items[item_id] = item
         return self._items.get(item_id)
 
     def set(self, item: T) -> None:
         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)
+        if item_id in self._items:
+            # If item already exists, remove it and add it to the end
+            self._items.pop(item_id)
+        elif len(self._items) >= self._max_items:
+            # If cache is full, evict the least recently used item
+            self._items.popitem(last=False)
+        self._items[item_id] = item
         self._on_changed(item)
 
     def delete(self, item_id: str) -> None:
-        # Both of these are no-ops if the item doesn't exist.
+        # This is a no-op 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)