Poll conditional orders + Allow custom logic to delay checks to a given date, block, or forever

[anxolin]

Implement some basic Polling Also, applies some follow-ups from: comments in https://github.com/cowprotocol/cow-sdk/pull/147

Implement a Polling (as a Template Method in ComposableCow)

This generic polling logic will check the following:

• 1. Validate concrete order: The order might have wrong parameters (or malformed ones). This method verifies it. In case it fils it will describe what was the issue (returns a reason).
• 2. Poll validate: Let's concretely order apply some polling validation. It will return undefined if the polling checks should continue, otherwise it will instruct that is not time to create an order. For this, it can signal:
  • 2.1 TRY_NEXT_BLOCK: This block is not good, but next one might
  • 2.2 TRY_ON_BLOCK: This block is not good, but try again in the given blockNumber
  • 2.3 TRY_AT_DATE: This block is not good, but try again after a given date
  • 2.4 DONT_TRY_AGAIN: This block is not good, but also the following blocks. Please don't try again because it will keep not being the right time!
• 3. Is Authorised: Verify if the owner authorised the order
• 4. Lastly, CALL getTradeableOrderWithSignature: Last check is to call and obtain the order. Ideally, most of the errors should have been handled before calling this function, this way, we only do this call when we are almost sure it will succeed.

isAuthorised

Method in ComposableCow to check if the order is authorised.

Exposed as public method, but also convenient for the polling logic.

Removed validation from constructor

I thought it was best to not do a validation in the constructor of the order, so we can programmatically call to isValid

Also the method isValid doesn't throw any more, instead returns the reason. This reasons are convenient for other methods like poll to give a good description of why the order is not yet ready.

Now polling can instruct to never poll again that smart order, and return a good reason why:

Generics for ConditionalOrders

Changed back to T and P as suggested in https://github.com/cowprotocol/cow-sdk/pull/147

Not implemented in this PR (follow up coming)

Custom logic in Twap conditional order to postpone some checks for the future (instead of checking on each block)

I left some TODOs:

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[coveralls]

coverage: 77.586% (-3.8%) from 81.422% when pulling e7f2ae07262792838a417d620ac4cccc2ef2dd19 on poll-conditional-orders into a4c398c21f8431469f9f67b9e097def78481525a on small-nit-suggestions.

[alfetopito]

Unit tests are not happy

[alfetopito]

@anxolin unit tests were still broken