Add testnet4 support

[Impa10r]

lnd and cln now support testnet4 lightningnetwork/lnd#9620, ps should too

[YusukeShimizu]

It appears that the same consideration is necessary for validateNetwork as well.
https://github.com/ElementsProject/peerswap/blob/master/swap/messages.go#L123

Could you please check if the swap is functioning properly?

Also, could you handle the corresponding change on the CLN side? It seems that support for testnet4 was recently added ElementsProject/lightning#8171.

[Impa10r]

thanks. updated and confirm working with lnd. struggling to test with cln so far: #370

[Impa10r]

tested swaps between LND and CLN, thanks to this PR: #371

[YusukeShimizu]

Would you mind reverting that merge commit and rebasing instead?

[Impa10r]

Would you mind reverting that merge commit and rebasing instead?

took a few tries with chatgpt, but I think I finally got what you asked. thanks for teaching me something new! the branch works fine with cln and lnd...

[YusukeShimizu]

LGTM.
The changes are limited to non-production areas (tests), so there’s no impact on runtime behavior or mainnet-facing code. All checks pass, so I’m approving.