Provide a more convenient method - getOnlyValue

[du zhilin]

When I call getOnlyValue(), it will first query all the results.

I expected getOnlyValue() to be called, which behaves the same as limit(1).getOnlyValue().

[Jinq]

I've followed your suggestion from elsewhere and overridden findFirst() that's already defined in Stream. findFirst() will call limit() before returning the expected result.

I've made this change to the 2.0 version of Jinq, which is pending release until someone says they specifically need a version of Jinq that uses the new jakarta.* packages. If you need me to backport this change to the 1.* release of Jinq, just let me know, and I can do that.