Make miners cache mined item

Saves two chunk+tile lookups per update, and one chunk+tile lookup per
draw.

src/js/game/components/miner.js

@@ -15,6 +15,7 @@ export class MinerComponent extends Component {
         return {
             lastMiningTime: types.ufloat,
             chainable: types.bool,
+            minedItem: types.nullable(types.obj(gItemRegistry)),
             itemChainBuffer: types.array(types.obj(gItemRegistry)),
         };
     }
@@ -22,12 +23,15 @@ export class MinerComponent extends Component {
     duplicateWithoutContents() {
         return new MinerComponent({
             chainable: this.chainable,
+            minedItem: this.minedItem
         });
     }
 
     /**
+     * 
+     * @param {{chainable?: boolean, minedItem?: BaseItem}} param0 
      */
-    constructor({ chainable = false }) {
+    constructor({ chainable = false, minedItem = null }) {
         super();
         this.lastMiningTime = 0;
         this.chainable = chainable;
@@ -38,6 +42,11 @@ export class MinerComponent extends Component {
          * @type {Array<BaseItem>}
          */
         this.itemChainBuffer = [];
+
+        /**
+         * @type {BaseItem}
+         */
+        this.minedItem = minedItem;
     }
 
     /**