Wrapper around the "real" batch function used by batch_keep_span

Takes the passed span and sets it as the active one, then calls the original batch function with the original parameter.

@spec batch_keep_span(
  Absinthe.Middleware.Batch.batch_fun(),
  any(),
  Absinthe.Middleware.Batch.post_batch_fun()
) :: {:middleware, Absinthe.Middleware.Batch, term()}

Works like Absinthe.Resolution.Helpers.batch, but preserves the active span.

The function supplied to the batch helper is executed in a Task by Absinthe, which means that the erlang opentelemetry SDK would lose track of the currently active span, because they are kept in a pdict.

To work around this, you can just replace batch with batch_keep_span, and the active span will be automatically passed and reset as the active one inside the batch function.