Protocol for resolving ForeignSuspend values across different platforms.

The protocol dispatches on the payload field of the first ForeignSuspend in the list. Consumers implement this protocol for their payload type to resolve foreign suspensions via platform-specific mechanisms (e.g., JS Promises, OS I/O completion ports).

The protocol uses continuation-passing style — the implementation calls continuation.(resolved) with a map of %{suspend_id => resolved_value} when ready, enabling both synchronous and asynchronous resolution.

Example (synchronous, for tests)

defmodule MyPayload do
  defstruct [:value]
end

defimpl Skuld.ForeignResolver, for: MyPayload do
  def await_resolutions(suspends, continuation) do
    resolved = Map.new(suspends, &{&1.id, &1.payload.value})
    continuation.(resolved)
  end
end

Example (async, for Hologram)

defimpl Skuld.ForeignResolver, for: Hologram.JS.PromiseRef do
  def await_resolutions(suspends, continuation) do
    promises = Enum.map(suspends, & &1.payload.promise)
    JS.Promise.all(promises).then(fn results ->
      resolved =
        suspends
        |> Enum.zip(results)
        |> Map.new(fn {s, val} -> {s.id, val} end)

      continuation.(resolved)
    end)
  end
end