Wait until all streams fail or reach the end.
pub fn fillRemaining(mr: *MultiReader, timeout: Io.Timeout) Io.Batch.AwaitConcurrentError!void
pub fn fillRemaining(mr: *MultiReader, timeout: Io.Timeout) Io.Batch.AwaitConcurrentError!void {
while (fill(mr, 1, timeout)) |_| {} else |err| switch (err) {
error.EndOfStream => return,
else => |e| return e,
}
}