bug: heliaInstance.libp2p.addEventListener('peer:discovery', cb) calls cb twice for same peer

[SgtPooki]

Using libp2p 0.42.2 via https://cdn.jsdelivr.net/npm/[email protected]/dist/index.min.js

Peer discovery should only emit once, unless we are in fact discovering the peer twice via different methods somehow.

Either way, once a peer is discovered, we should cancel any in-progress operations and emit that we discovered the peer only once.

While working on a new helia-script-tag example (via #43), I was able to get the following event log:

1263ms - Created LibP2P instance
1263ms - Created Helia instance
2248ms - Discovered peer QmNnooDu7bfjPFoTZYxMNLWUQJyrVwtbZg5gBMjTezGAJN
2252ms - Discovered peer QmNnooDu7bfjPFoTZYxMNLWUQJyrVwtbZg5gBMjTezGAJN
2252ms - Discovered peer QmQCU2EcMqAqQPR2i9bChDtGNJchTbq5TbXJJ16u19uLTa
2252ms - Discovered peer QmQCU2EcMqAqQPR2i9bChDtGNJchTbq5TbXJJ16u19uLTa
2253ms - Discovered peer QmbLHAnMoJPWSCR5Zhtx6BHJX9KiKNN6tpvbUcqanj75Nb
2254ms - Discovered peer QmbLHAnMoJPWSCR5Zhtx6BHJX9KiKNN6tpvbUcqanj75Nb
2254ms - Discovered peer QmcZf59bWwK5XFi76CZX8cbJ4BhTzzA3gU1ZjYZcYW3dwt
2254ms - Discovered peer QmcZf59bWwK5XFi76CZX8cbJ4BhTzzA3gU1ZjYZcYW3dwt
74326ms - Connected to QmbLHAnMoJPWSCR5Zhtx6BHJX9KiKNN6tpvbUcqanj75Nb
77805ms - Connected to QmcZf59bWwK5XFi76CZX8cbJ4BhTzzA3gU1ZjYZcYW3dwt
135298ms - Disconnected from QmbLHAnMoJPWSCR5Zhtx6BHJX9KiKNN6tpvbUcqanj75Nb
138782ms - Disconnected from QmcZf59bWwK5XFi76CZX8cbJ4BhTzzA3gU1ZjYZcYW3dwt

replaces ipfs/helia#56

[SgtPooki]

You can see this in action at https://codesandbox.io/p/sandbox/helia-script-tag-g420c3, with PR to helia-examples repo at ipfs-examples/helia-examples#13