feat(snapshot): testing examples

[zjp-CN]

1. add testing bash scripts for examples
2. add src/test.rs which takes snapshots for:

• calc & mechanic: succeeded
• mlua & api: failed #54

---

And

• fix the mechanic example
• add mlua vendored feature in the absence of Lua

[zjp-CN]

You can use these cmds in examples dir:

• cargo test
• cargo insta test --review to update all the snapshots (except tagged with #[ignored] ones).
• cargo insta test --review -- test_fn_name to update test_fn_name only

[zjp-CN]

Will you consider merging this PR?

[noib3]

Sorry I have yet to review it, will try to look at it this weekend.

[zjp-CN]

I'm gonna close this and put up a new PR to test examples.