[FEATURE] Fused NEON WaveNet engine for AArch64 (Apple Silicon) #657

There is an opportunity to reduce further the CPU load of the models on Apple Silicon.

This PR against Core provides a material speedup.

Tested on MacBook Air M2 and iPhone 17.
On M2, a2_fast benchmarks at 29x RT and 'fused' at 50x RT
Non-scientific testing with REAPER yielded around ~1.27× lower load

PR #656 against this Plugin repo adds flags to enable that Core optimisation.