bug: Inconsistency in Order not Valid semantics

[anxolin]

Problem

Currently, we re-try on every block for INVALID ORDERS, however this is incoherent with how we handle the error in the SDK

See here: https://github.com/cowprotocol/cow-sdk/blob/main/src/composable/ConditionalOrder.ts#L260

And the TEST: https://github.com/cowprotocol/cow-sdk/blob/main/src/composable/ConditionalOrder.spec.ts#L246

Here we have a bunch of validations we do for TWAPs, where isValid means, the order has some parameters that are wrong, so there's no point to poll in the future: https://github.com/cowprotocol/cow-sdk/blob/main/src/composable/orderTypes/Twap.spec.ts#L135

For this reason, I created this PR to make sure we stop watching the order #105

Proposal

The proposal is to make it more explicit in the doc that watch tower will stop indexing for any of the below errors except POLL_TRY_NEXT_BLOCK, POLL_TRY_AT_BLOCK or POLL_TRY_AT_EPOCH

# Watch Tower will check at the instructed time
POLL_TRY_NEXT_BLOCK: PollTryNextBlock(string)
POLL_TRY_AT_BLOCK: PollTryAtBlock(uint256,string)
POLL_TRY_AT_EPOCH: PollTryAtEpoch(uint256,string)

# Watch Tower will stop polling the order for future blocks
POLL_NEVER: PollNever(string)

# Effectivelly same as `POLL_NEVER` but with specific semantics on what's the reason to stop polling
PROOF_NOT_AUTHED: ProofNotAuthed()
SINGLE_ORDER_NOT_AUTHED: SingleOrderNotAuthed()
SWAP_GUARD_RESTRICTED: SwapGuardRestricted()
INVALID_HANDLER: InvalidHandler()
INVALID_FALLBACK_HANDLER: InvalidFallbackHandler()
INTERFACE_NOT_SUPPORTED: InterfaceNotSupported()
ORDER_NOT_VALID: OrderNotValid(string) 

Therefore, in particular ORDER_NOT_VALID should translate to a POLL_NEVER

🚨 Blocker: We can't make it coherent right now

Currently, there's an order for safe 0xAB8E66516e189ECf57415562183584659A814e4b which is meant to be checked in every block, but it raises the error ORDER_NOT_VALID instead of POLL_TRY_NEXT_BLOCK.

TO DO:

• We could add an exception for this order, or ask nicely to the dev to use POLL_TRY_NEXT_BLOCK if that's the behaviour they seek
• Document nicely so DEVs have the above mentioned behaviour clear
• Merge fix: drop invalid orders #105

[mfw78]

Can this be closed given the new documentation on polling?