Immediately unref the `ref` provided to `createRpcStream()`

[vweevers]

Copied from Level/party#28 (comment): we don't initially unref. You must make at least one db operation for the logic to work. So this hangs:

const name = Date.now().toString()

const db1 = party(name)
const db2 = party(name)

await db1.open()
await db2.open()

console.log('opened')

// Comment this out to not make the event loop hang
// await db1.put('a', 'b')
// console.log(await db2.get('a'))

[vweevers]

On second thought, it might make more sense to do this (i.e. deciding the initial unref/reffed state) in level-party.