Val should not extends Lazy by default

[He-Pin]

I know the Lazy is used for optimize performance, but the:

• Boolean.FALSE
• Boolean.TRUE
• Null

are constant values, but now it has a cached field value from the Lazy.

I think a better result is that we have an interface for value, eg:

• trait Eval
• trait CoEval extends Eval
• trait LazyEval extends Eval

We can rename the Lazy to LazyEval.