feat: add sendMultiPayment function and example

[rolznz]

This adds a dependency on lightning-tools to decode invoices, since the current spec returns payment hashes by default.
Or we could remove the dependency and generate ids and pass them to do the mapping, maybe that's better. UPDATE: using id field of nwc to map instead of payment hash

The idea is that you can pay multiple invoices in a single request, but you need to know which ones succeeded and which ones failed. I was thinking an object like:

{
  payments: [
    {
      paymentRequest: 'lnbc...',
      preimage: '7c2c....'
    },
    ...,
  ],
  errors: [{
     paymentRequest: 'lnbc...',
     message: "Insufficient balance".
     code: 1234
  }]
}

Note: the error handling isn't done yet

[socket-security]

New dependencies detected. Learn more about Socket for GitHub ↗︎

Package	New capabilities	Transitives	Size	Publisher
npm/@getalby/lightning-tools@5.0.1	network	0	134 kB	reneaaron

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[rolznz]

Update: we need to work on some other things like splitting the NWC client from the WebLN client. I will mark this method as unconfirmed until it is properly added to WebLN and the Alby extension