sdk-core: Destroy client on dispose (#235)

* sdk-core: Destroy client via the dispose method

* Undo metrics setup for node example

Author: konraddysput

packages/sdk-core/src/BacktraceCoreClient.ts

@@ -343,6 +343,8 @@ export abstract class BacktraceCoreClient<O extends BacktraceConfiguration = Bac
                 module.dispose();
             }
         }
+
+        BacktraceCoreClient.destroy();
     }
 
     protected addModule<T extends BacktraceModule>(module: T): void;
@@ -402,4 +404,8 @@ export abstract class BacktraceCoreClient<O extends BacktraceConfiguration = Bac
             sessionFiles: this.sessionFiles,
         };
     }
+
+    private static destroy() {
+        this._instance = undefined;
+    }
 }