ESM support

[vimwitch]

To support ethers 6 and hardhat 2.14 we need to import ESM modules. Big libraries in the ecosystem are moving to ESM so I think we can/should do the same. If we export an ESM module anyone using commonjs with not be able to import the unirep libraries. I think this is reasonable at this point given that nodejs, webpack, and browsers all support ESM out of the box.

Typescript support for ESM is mediocre at this point. The configuration is complicated, especially with tests/ts-node. I think this is a good opportunity to remove some parts of our systems that are typescript, specifically:

• switch @unirep/contracts deploy/build/test logic to javascript
  • manually write a type definition for the deploy function

This issue is a pretty big lift and I think we should break it up into the following steps:

1. Remove typechain support in @unirep/contracts
2. Refactor @unirep/contracts to javascript
   • Manually write a type definition file for the deploy function
3. Switch @unirep/core to ESM and ethers-v6
4. (optional) switch @unirep/utils and @unirep/circuits to ESM

Related #366

[vimwitch]

@vivianjeng let me know what you think of this

[vivianjeng]

yeah I think we can support v6 first
and then figure out if there is another way to switch back to ts (I think it might be possible)