Feat/bancor v2

[xianny]

Description

Add integration for Bancor V2.

contracts/asset-proxy

• BancorBridge contract and tests

asset-swapper

• BancorService (wrapper for the Bancor SDK)
• tests for BancorService against mainnet and real Bancor network
• refactor of SourceQuoteOperation to return one fillData per sample instead of one fillData per source

contract-addresses

• added bancorBridge field

We're waiting on https://github.com/bancorprotocol/sdk/pull/20 to merge and publish before we enable Bancor as a source. After the SDK is updated, we need to do the following:

• [ ] Deploy BancorBridge contract and then update @0x/contract-addresses
• [ ] Add Bancor to list of valid Sell sources in .../market_operation_utils/constants.ts
• [ ] Privately publish and AB test on staging/prod

Testing instructions

I tested with simbot using https://github.com/dorothy-zbornak/0x-swap-server. Charts are in a comment below.

Unit tests are updated.

Types of changes

• New feature (non-breaking change which adds functionality)

Checklist:

• [x] Prefix PR title with [WIP] if necessary.
• [x] Add tests to cover changes as needed.
• [x] Update documentation as needed.
• [x] Add new entries to the relevant CHANGELOG.jsons.

[xianny]

Simbotted with Bancor enabled in https://github.com/dorothy-zbornak/0x-swap-server and got some data:

No surprise here.

Bancor revert rate a bit worrying.

Bancor slippage also higher than the rest.

Bancor TOKEN slippage is good though. Maybe we enable Bancor only for BNT for now??

Just for the record.

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A-B testing with prod:

[xianny]

With latest asset-swapper (Bancor disabled)

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Little bit worried about Balancer reverts looking uneven so I ran it for a while with just Balancer and Uniswap as sources:

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