chore: optimisation and fix for clipping and blend modes

[GoodBoyDigital]

Refactored things a bit to make them run faster and a few other bits!

• 30% faster than the current v8 (which was faster than v7 already!)
• uses less memory, about 25% than current v8
• Better validation of spine updates, if the meshes / draw order remain the same then no rebuild is triggered
• spine bone / attachment updates only happen once per state update at the point the data is needed (eg measuring or rendering). No heavy lifting if state is not updated
• Added support for blend modes
• Fixed clipping - so it works properly now (and is faster more memory efficient)

[GoodBoyDigital]

cc @badlogic. would be great to get your eyes on this one if you get a mo! Cheers!