feat req: assign witness parallelly

[lispc]

95% of rows are used for point mul_scalar. So we can assign witness like this ?

// whenever mul_scalar is used
// launch a new thread 
thread::new( | offset, point, scalar| {
// assign mul scalar witness
})
offset += 79xxx; // a prefined value
// assign other witness 

[xgaozoyoe]

I am working on it.