fix: making endings clear and final.

[martinheidegger]

This is an attempt to add clear end operations to streamx.

If .push(null) or .end() are called for a second time, streamx will now throw an Error alerting the user to that misuse of the API.
This PR fixes some incompatibility with Node.js (.writable becomes false after end).

Closes #44, #45

[pfrazee]

This PR fixes some incompatibility with Node.js (.writable becomes false after end).

I just ran into this issue myself. I monkey patched around it with this:

// HACK
// this is a specific issue that's waiting on https://github.com/streamxorg/streamx/pull/46
// -prf
hyperswarmSocket._ended = false
const _end = hyperswarmSocket.end
hyperswarmSocket.end = function (data: any) {
  _end.call(this, data)
  this._ended = true
}
Object.defineProperty(hyperswarmSocket, 'writable', {
  get() {
    return !this._ended && this._writableState !== null ? true : undefined
  }
})

[martinheidegger]

Rebase to the latest changes, though it looks like 9d3eed0 defines the current behavior as desired.

[mafintosh]

main does a check