Bug: second payment to CLN offer fails

[orbitalturtle]

Describe the bug

When trying to pay a CLN offer twice, CLN sends us the same invoice for the second payment, causing LND to error. The solution is likely that we're using the same key to sign each invoice request, but we should use a new one each time:

lndk/src/lndk_offers.rs

Line 177 in 6132601

let pubkey_bytes = signer

Thanks to @jkczyz for figuring out what was going on here!

[orbitalturtle]

I have a local branch working that fixes this. I just need to push it up.