Simplify channel handshake logic to not involve retry

[soareschen]

Description

This is a follow up on #1066. I have refactored the logic in do_chan_open_ack_confirm_step so that it completes the full handshake without having to rely on the error retry loop.

The issue of using the same error retry loop for intentional retry is that the delay set in the error retry also affects the intentional retry. For the case of do_chan_open_finalize_with_retry, when do_chan_open_ack_confirm_step returns PartialOpenHandshake, the retry_with_index function will only try the next handshake step after the delay set in the fibonacci delay timer. This can significantly slow down the relayer if we do too many of such retries.

A better strategy is to explicitly write down the expected state transition, especially given that our state machine is pretty small. This also helps improve the readability, as readers do not need to understand the state machine defined else where in order to understand how the code works.

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For contributor use:

• Updated the Unreleased section of CHANGELOG.md with the issue.
• If applicable: Unit tests written, added test to CI.
• Linked to Github issue with discussion and accepted design OR link to spec that describes this work.
• Updated relevant documentation (docs/) and code comments.
• Re-reviewed Files changed in the Github PR explorer.

[adizere]

LGTM!