Optimize Coinswap: Use a Single Funding and Contract tx for Efficiency

[KnowWhoami]

Current Scenario:

• Let's say taker wants to perform coinswap with tx_count= 3 on each step.
• tx_count = 3 means that each peer participating in the coinswap has to break the forwarding amount in 3 random values and create a seperate funding tx for each of them.

This introduces several edge cases which are as follows:

• A peer must have at least 3 utxos in its wallet in order to create 3 seperate funding txes otherwise they can't forward and coinswap would fail..
• Taker has to pay the mining fees of all the funding txes which are being created during this coinswap and in case of unsuccesfull swap , each peer has to broadcast its own 3 contract txes as each of them aims to spend just a single funding utxo which makes the whole protocol expensive whether it went successful or not..

Proposed Solution:

• Only a single funding transaction should be created, generating tx_count + 1 UTXOs (accounting for change, if applicable). Similarly, a single contract transaction should be created to spend this funding UTXO.

[mojoX911]

Added pointers:

• These tx_count (we should give a more apt name) number of utxos should be created with random amounts utilizing randomize amounts and fees #432
• As an optional feature, we can add payjoin like input mixing between the swap partners in the funding txs. This increases fees slightly, but adds further ambiguity in the flow.
• Corollary feature: the wallet should automatically maintain a random but well-distributed utxo set, which can be intelligently used to mix both inputs and outputs. This will make payjoining very effective and easy through out the swap market.

[khadar1020]

I would like to work on this issue

[mojoX911]

This is not up for grab immediately. This will require quite a lot of thinking and designing. This will also be done over various preliminary works, which are yet to come. If you are interested feel free to join our dev calls (community link in the readme).