Overhaul CPU backend

• Support parallel & vector codegen for CPU backend
• Rewrite runtime proc macro to be simpler
• Rework dot & matmul examples

requested review from @aaronjc4

assigned to @rarbore2

added 5 commits

• 53fa3951...0783d875 - 4 commits from branch main
• fe49d8c2 - Merge branch 'main' into parallel_cpu

Compare with previous version

mentioned in commit e0634614

merged