fix: waitForSync('full') should resolve even if the device being synced doesn't have sync capability for all namespaces

Description

I think the current implementation of waitForSync() will not work if one of the devices does not have sync capability for one or more namespaces. We should at least have a test for this, and if it fails we need a fix, which I think might be:

function isSynced(state, namespaces, peerSyncControllers) {
  for (const ns of namespaces) {
    let syncablePeers = 0
    for (const psc of peerSyncControllers.values()) {
      const { peerId } = psc
      if (psc.syncCapability[ns] === 'blocked') continue
      if (!(peerId in state[ns].remoteStates)) return false
      if (state[ns].remoteStates[peerId].status === 'connecting') return false
      syncablePeers++
    }
    if (syncablePeers > 0 && state[ns].dataToSync) return false
  }
  return true
}

This came up reviewing #410

Start at the JavaScript implementation of waitForSync() and its isSynced() helper; trace how peerSyncControllers, syncCapability, and remoteStates are represented. Add a regression test for a device blocked for some namespaces, then run the relevant test suite and confirm waitForSync('full') resolves when all eligible namespaces are synchronized.