Left matmul 100x performance improvements #208

Job	Run time
build (windows-latest, Debug)	34s
build (ubuntu-latest, Release)	18s
build (macos-latest, Debug)	16s
build (ubuntu-latest, Debug)	11s
build (macos-latest, Release)	11s
build (windows-latest, Release)	28s
	1m 58s

Provide feedback