FEATURE: Replace mulmod + Optimize Primality

[guntas-13]

replace the iteration-based mulmod() with math/bits.Mul64 + math/bits.Div64

[guntas-13]

as per PR #6 this is wayyy good - could also for even faster build a lookup table and work with that - Anyways with both - that is not the point of the whole project - Prime finding was a just a demonstration that such parallelized workloads could be written easily utilizing our built AFS