snowbridge: improve destination fee handling to avoid trapping fees dust

[acatangiu]

On messages Ethereum -> Polkadot Asset Hub: whether they are a token transfer or a Transact for registering new token, make sure to handle unspent fees, rather than trapping them.

This PR deposits them to Snowbridge's sovereign account on Asset Hub.

[acatangiu]

cc @vgeddes, @alistair-singh, @claravanstaden, @yrong

[paritytech-cicd-pr]

The CI pipeline was cancelled due to failure one of the required jobs. Job name: test-linux-stable 2/3 Logs: https://gitlab.parity.io/parity/mirrors/polkadot-sdk/-/jobs/7236477

[yrong]

In https://github.com/paritytech/polkadot-sdk/pull/4175 we only cover the trapping on AH, thanks for the fix.

Btw:

cargo test -p bridge-hub-rococo-integration-tests --lib tests::snowbridge::send_token_from_ethereum_to_penpal  -- --nocapture

failed with the error

2024-09-04T05:57:38.016390Z TRACE xcm::execute: Message executed result=Err(ExecutorError { index: 3, xcm_error: FailedToTransactAsset("Account cannot exist with the funds that would be given"), weight: Weight { ref_time: 1000000000, proof_size: 65536 } })

I think we may need to increase the destination_fee on penpal or a lower ED here could also work.

[acatangiu]

I think we may need to increase the destination_fee on penpal

Yes, and once this change is deployed you also need to check this in UIs in production, to avoid failures for users.

Check that beneficiary on final dest either:

• has existing account satisfying ED,
• current transfer adds enough destination_fee to also cover ED.

cc @alistair-singh

[paritytech-cmd-bot-polkadot-sdk[bot]]

Created backport PR for stable2407:

• 5819 with remaining conflicts!

Please cherry-pick the changes locally and resolve any conflicts.

git fetch origin backport-5563-to-stable2407
git worktree add --checkout .worktree/backport-5563-to-stable2407 backport-5563-to-stable2407
cd .worktree/backport-5563-to-stable2407
git reset --hard HEAD^
git cherry-pick -x 62534e53eaeabe021de6fbe9ad51fa0e160a56c5
git push --force-with-lease

[paritytech-cmd-bot-polkadot-sdk[bot]]

Successfully created backport PR for stable2409:

• 5820