feat(layered-storage): simplify

BREAKING CHANGE: Most stuff was changed.

This is a really big overhaul that greatly reduces the API and the
codebase. This should be much easier to maintain and also more
performant when used at the expense of removing support for some niche
features.

src/layered-storage/common.ts

@@ -1,13 +1,15 @@
 export type KeyRange = number | string | symbol;
-export type KeyValueLookup = Record<KeyRange, any>;
 export type LayerRange = number;
 export type Segment = boolean | number | object | string | symbol;
-export type KeyValueEntry<KV extends KeyValueLookup> = {
-  [Key in keyof KV]: readonly [Key, KV[Key]];
-}[keyof KV];
-export type FilteredKeyValueEntry<
-  KV extends KeyValueLookup,
-  Keys extends keyof KV
+
+export type KeyValueLookup<Keys extends KeyRange> = Record<
+  Keys,
+  boolean | number | object | string | symbol
+>;
+
+export type KeyValueEntry<
+  KV extends object,
+  Key extends keyof KV = keyof KV
 > = {
-  [Key in Keys]: readonly [Key, KV[Key]];
-}[Keys];
+  [Key in keyof KV]: readonly [Key, KV[Key]];
+}[Key];