fix: parse buy txid from midgard actions

[kaladinlight]

Description

The previous double swap logic was incorrect resulting in rune swaps polling the wrong txid against the wrong chain. This logic removes the double swap condition and instead just attempts to get the latest txid specified in the outbound transactions array. This will evaluate in three different ways:

• Single outbound transaction is rune (asset -> rune): which will return the sellTxId and rely on the swap status for confirmation (sellTxId doesn't appear to actually be used in the downstream logic due to the hasOutboundTx variable in swapper endpoints.ts)
• Single outbound transaction is asset (asset or rune -> assest): which will return the outbound txid for the buy chain to poll for status
• Double swap transaction (asset -> asset): which will return sellTxId on the first rune swap outbound and rely on swap status which will be pending, and then wait for the final outbound asset tx and return the txid for the buy chain to poll status for

Pull Request Type

• 🐛 Bug fix (Non-breaking Change: Fixes an issue)
• 🛠️ Chore (Non-breaking Change: Doc updates, pkg upgrades, typos, etc..)
• 💅 New Feature (Breaking/Non-breaking Change)

Issue (if applicable)

N/A

Risk

High Risk PRs Require 2 approvals

Medium - this changes transaction confirmation logic

What protocols, transaction types or contract interactions might be affected by this PR?

Thorchain Swaps

Testing

• Ensure the following swaps confirm:
  • rune -> asset
  • asset -> rune
  • asset -> asset
  • asset -> asset streaming (results in double swap it seems which I didn't have enough funds to test myself)

Engineering

☝️

Operations

☝️

Screenshots (if applicable)

[gomesalexandre]

Logic looks sane conceptually.

Tested at runtime and spotted no regressions in THOR swapper status polling:

• L1 -> RUNE

• RUNE -> L1

• L1 -> L1

• L1 - L1 streaming swap

Untested

[gomesalexandre]

Retested locally:

• L1 -> RUNE

• RUNE -> L1

• L1 -> L1