default Tuple2<Optional<T>, Seq<T>> splitAtHead() {
        return splitAtHead(this);
    }
Split a stream at the head.
<p>
<pre><code>
// tuple(1, (2, 3, 4, 5, 6))
Seq.of(1, 2, 3, 4, 5, 6).splitHead(3)
</code></pre>

@see #splitAt(Stream, long)
jOOL-java-8/src/main/java/org/jooq/lambda/Seq.java