NEW FAST DECODE MODE

New fast-decode (2) to allow for an average AV1 software cycle reduction of 25-50% vs fast-decode 0 with a 1-3% BD-Rate loss across the presets

Improved fast-decode (1) option to increase its AV1 software cycle reduction by ~10% while maintaining the same quality levels

Improved --lp settings for high resolutions, with CRF gaining a ~4% improvement in speed and VBR gaining ~15%

Further Arm-based optimizations improving the efficiency of previously written Arm-neon implementations by an average of 30%

Address speed regressions for high resolutions first pass encode by tuning the threading parameters, with 1080p showing the biggest gains

Enabled AVX512 by default in cmake allowing for ~2-4% speedup

...and more