Left matmul 100x performance improvements (#44) #213

Job	Run time
build (ubuntu-latest, Release)	12s
build (macos-latest, Release)	18s
build (ubuntu-latest, Debug)	9s
build (windows-latest, Release)	34s
build (macos-latest, Debug)	17s
build (windows-latest, Debug)	32s
	2m 2s

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