Memoize some stores, improve room support

packages/store/src/collection.ts

@@ -1,6 +1,7 @@
 import {readable, derived, writable, Readable, Subscriber} from "svelte/store"
 import {batch, indexBy, remove, assoc, now} from "@welshman/lib"
 import {withGetter, ReadableWithGetter} from "./getter.js"
+import {memoized} from "./memoize.js"
 
 // Collection utility
 
@@ -126,7 +127,7 @@ export const collection = <T>({name, store, getKey, load}: CollectionOptions<T>)
     // store will update when it arrives
     loadItem(key, relays)
 
-    return derived(indexStore, $index => $index.get(key))
+    return memoized<T | undefined>(derived(indexStore, $index => $index.get(key)))
   }
 
   const onItem = (cb: Subscriber<T>) => {

packages/store/src/index.ts

@@ -1,6 +1,7 @@
 export * from "./synced.js"
 export * from "./getter.js"
 export * from "./throttle.js"
+export * from "./memoize.js"
 export * from "./custom.js"
 export * from "./repository.js"
 export * from "./collection.js"

packages/store/src/memoize.ts

@@ -0,0 +1,8 @@
+import {Readable, Subscriber} from "svelte/store"
+import {memoize} from "@welshman/lib"
+
+export const memoized = <T>(store: Readable<T>) => {
+  const {subscribe} = store
+
+  return {...store, subscribe: (f: Subscriber<T>) => subscribe(memoize(f))}
+}