feat: async peerstore backed by datastores (#1058)

We have a peerstore that keeps all data for all observed peers in memory with no eviction.

This is fine when you don't discover many peers but when using the DHT you encounter a significant number of peers so our peer storage grows and grows over time.

We have a persistent peer store, but it just periodically writes peers into the datastore to be read at startup, still keeping them in memory.

It also means a restart doesn't give you any temporary reprieve from the memory leak as the previously observed peer data is read into memory at startup.

This change refactors the peerstore to use a datastore by default, reading and writing peer info as it arrives.  It can be configured with a MemoryDatastore if desired.

It was necessary to change the peerstore and *book interfaces to be asynchronous since the datastore api is asynchronous.

BREAKING CHANGE: `libp2p.handle`, `libp2p.registrar.register` and the peerstore methods have become async

src/dialer/dial-request.js

@@ -63,7 +63,10 @@ class DialRequest {
     tokens.forEach(token => tokenHolder.push(token))
     const dialAbortControllers = this.addrs.map(() => {
       const controller = new AbortController()
-      setMaxListeners && setMaxListeners(Infinity, controller.signal)
+      try {
+        // fails on node < 15.4
+        setMaxListeners && setMaxListeners(Infinity, controller.signal)
+      } catch {}
 
       return controller
     })