Deprecate executedSurplusFee, adding executedFee and executedFeeToken

[iamacook]

Summary

executedSurplusFee is being deprecated, in favour of executedFee and executedFeeToken. This deprecates the formers, and adds the latter to Orders.

Eventually, the executedFeeToken will also need updating as it will will be expressed in SURPLUS tokens (BUY tokens for SELL orders and SELL tokens for BUY orders). For now, it remains the sellToken.

Note: all fields are no longer nullable, apart from previewed TWAP parts.

Changes

• Add executedFee/executedFeeToken to OrderSchema.
• Add fields to relevant swap/TWAP entities, removing wrong nullable properties.
• Map new fields in respective swap/TWAP mappers.
• Update builder to use same values for executedSurplusFee<>executedFee and sellToken<>executedFeeToken.
• Update tests accordingly.

[iamacook]

CoW confirmed that none of these are nullable.