`tuple_data_t` micro-optimization

[behdad]

Are we always sure that indices and x_deltas and y_deltas if available, have the same length? Ie. no allocation failure? If yes we can use arrayZ in operator *=, operator +=, and possibly other places.

[behdad]

Same in compile_deltas when rounding.

[qxliu76]

Yes, I think so, I'll work on this.