impl AIP#31 changes to Payout

[elpiel]

Changes

get_payout() - Progress has been made in #313 however there are still work to be done to ensure it's aligned with JS

• Makes Payout is prone to overflow #291 redundant
• JS reference impl: https://github.com/AdExNetwork/adex-validator/blob/master/services/sentry/lib/getPayout.js

TODOs:

• Double check input for targeting rules:

https://github.com/AdExNetwork/adex-validator-stack-rust/blob/73683e8f38f12e497e8f8a38632378767f4dfdf9/sentry/src/payout.rs#L52-L76

• Tests with targeting_rules set on Channel::targeting_rules or ChannelSpec::targeting_rules

[elpiel]

@simzzz did you check out all the TODOs for the targeting input? Meaning: To check if all of them should be set or not when the payout needs to calculate the targeting input.

PS: I see that the todos haven't been removed.

[elpiel]

All todos have been checked accordingly to @simzzz , closing this issue.
Todo comments will be removed with AIP#61 #377