auto loopin: consider settled invoices swap succeeded

[hieblmi]

This PR allows the auto loop-in dispatcher to continue with the execution of the next swap once a previous swap's invoice is settled.

Set parameters

loop --network regtest setparams --autoloop=true --autobudget 10000000 --maxamt 1000000 --feepercent 20 --autoinflight 10

Set rule

loop --network regtest setrule --type in --outgoing_threshold 99 node_key_to_loop_in_to

Result:
A new swap is dispatched although the previous swap is still in a pending state

LOOP_IN SUCCESS 0.003 BTC - P2TR: bcrt1p7awp9kaujtdr5h2pzlcpzyuypjsnh35trv5ma49mznfkl6yntntsh739lh (cost: server 130, onchain 7700, offchain 0)
LOOP_IN INVOICE_SETTLED 0.003 BTC - P2TR: bcrt1para8f4fy3r9qtrvvpmrf0z3uzwh776zv7577fsx24k8mvtxfagrqhp6w87 (cost: server -299870, onchain 7700, offchain 0)
LOOP_IN HTLC_PUBLISHED 0.003 BTC - P2TR: bcrt1pzapdkea2gamkf5f7p52lwhx0p55ry57g59qnyugxda6rn7m6295q6zpd9g

Accounting considerations:

To deal with pending swap fees the auto loop-in engine temporarily assigns pending swaps the maximum allowed fees so to not overshoot the set budget. Once the swap finalizes the actual fees(likely lower) will be set on the swap and the auto-loop dispatcher will reevaluate the creation of a new swap if it was previously blocked by an elapsed budget.
As an example, we could create many swaps in settled state that temporarily chew up our budget - but once the swaps finalize and capital frees new swaps might be dispatched.

[GeorgeTsagk]

Lgtm ⭐

[bhandras]

LGTM 🎉

[bhandras]

nit: perhaps consider adding a comment here explaining why we do this.