[Tip Request] Hydradx EVM support on subsquare

To support HydraDX EVM related features on subsquare, OpenSquare team did some customization development, including:

1. Research and learn code of HydraDX app to check how EVM works on HydraDX.
2. Deploy statescan and subsquare instances for parsing history EVM related extrinsics and testing.
3. Support metamask connect, singing and commenting. This request lots of code refactor to support both substrate and EVM addresses on a single network.
4. Support web2 user binding an EVM address.
5. Do address convertion between EVM address and substrate address to show them on UI and submit extrinsics.
6. In scan scripts, extract substrate calls from ethereum#transact extrinsic, so we can update referendum status in time when related calls detected.

Related fronted code PRs:
https://github.com/opensquare-network/subsquare/pull/3786
https://github.com/opensquare-network/subsquare/pull/4040
https://github.com/opensquare-network/subsquare/pull/3754

Cost

Roughly these features cost us 2 FTE 10 days work, 160 hours. Taking $80 per hour as the rate, it's $12,800. Considering these features can be used by other projects, we will request part of it. Our final request is 500k HDX.