Use Vitest instead of Mocha

[Yang-33]

When line-bot-sdk-nodejs supports ESM, we will use ESM code for testing. Vitest supports ESM+Typescript. This change will switch from using mocha to using vitest.

Also, along with mocha, nyc will be removed from dependencies because vitest supports coverage as well.

About the workaround:

1. Running vitest 1.4.0 results in TypeScript errors due to an issue with vite, which vitest uses. The latest version of vite has fixed this, so I explicitly added the latest vite to the dev dependencies.
   • type error | Type 'FSWatcher' is missing the following properties from type 'FSWatcher': ref, unref vitejs/vite#15714
2. Running vite for CJS leads to TypeScript errors due to an issue with rollup, which vite uses. There is no good workaround for CJS. I resolved this by rewriting node_modules as a workaround. There are no problems using vitest(?)
   • Cannot find module 'rollup/parseAst' or its corresponding type declarations. rollup/rollup#5199
   • Cannot find module 'rollup/parseAst' after vite 5 got released vitest-dev/vitest#4567

[Yang-33]

conflict is resolved by rebasing. Diff: https://github.com/line/line-bot-sdk-nodejs/compare/7dc13c564001e8ae3f99509f1f44f756ac33a681..4aedf2388021d9b85af970df683a6d50a921ba4e
thank you for review~