fix: fix declaration merging error

[whxaxes]

Checklist

• npm test passes
• tests and/or benchmarks are included
• documentation is changed or added
• commit message follows commit guidelines

Affected core subsystem(s)

Description of change

发现通过 declaration merging 的 override 方式还是有问题，会导致 export 出去的就只剩了一个 restore 方法，把原来的 EggMock 覆盖掉了，改回 restore: () => any。

[whxaxes]

@paranoidjk 貌似我错了.... declaration merging 不能绕过 override 的问题