Add support for generic srt socket options set/get.

[toots]

This PR adds support for generic SRT socket options:

• All srt socket types used in input.srt and output.srt are now bare bone srt.socket with no method. This decluters the API documentation.
• srt.socket is added to decorate a SRT socket with its methods
• A new on_socket callback is introduced that is executed just after setting our default socket options to give the user flexibility to set their own and/or monitor a socket etc.
• New socket options methods are added.

Here's an example use to set latency on incoming sockets. Please note that this is more tricky than it seems: setting the latency on the incoming socket instead of the listening socket results in a timeout!

def on_socket(~mode, s) =
  if
    mode == "listen"
  then
    s = srt.socket(s)
    print(
      "Setting latency to 20ms on listening socket"
    )
    s.set_latency(20)
  end

  if
    mode == "incoming"
  then
    s = srt.socket(s)
    print(
      "Incoming socket latency: #{s.latency()}ms"
    )
  end
end

input = input.srt(mode="listener", on_socket=on_socket)

Ref: #4256