feat: optimize img style

Author: SSShooter

src/index.less

@@ -245,6 +245,7 @@
     pointer-events: none;
     display: block;
     margin-top: 8px;
+    object-fit: cover;
   }
 
   .circle {

src/nodeOperation.ts

@@ -14,7 +14,7 @@ import {
 } from './utils/index'
 import { findEle, createExpander, shapeTpc } from './utils/dom'
 import { deepClone } from './utils/index'
-import type { Topic, Wrapper, CustomSvg } from './types/dom'
+import type { Topic, Wrapper } from './types/dom'
 import type { MindElixirInstance, NodeObj } from './types/index'
 import { LEFT, RIGHT, SIDE } from './const'