New node: top8bits

[Cyan4973]

This add a new node for numeric streams, top8bits, as a specialized variant of bitSplit.

It:

• determines the effective width of the numeric values
• split it in 2 parts, the top 8-bits on one side, and the lower bits on the other.

This is presumed useful in scenarios where predictability is concentrated on the top bits, but lower bits are essentially noise.

Also attempted to make it part of ace training