think about it is possible to migrate to pnpm and remove yarn support

[damingerdai]

like npm/yarn, pnpm is the next generation package manager.

It has four advantages：

1. Fast
   pnpm is up to 2x faster than the alternatives
2. Efficient
   Files inside node_modules are linked from a single content-addressable storage
3. Supports monorepos
   pnpm has built-in support for multiple packages in a repository
4. Strict
   pnpm creates a non-flat node_modules, so code has no access to arbitrary packages