Write and test uint64_t generator

[mmore500]

The function GetUInt64() draws uniformly over all possible uint64_t's, analogously to the function GetUInt().

I also added some tests for GetUInt().

[codecov]

Codecov Report

Merging #202 into master will decrease coverage by 0.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #202      +/-   ##
==========================================
- Coverage   65.05%   65.04%   -0.02%     
==========================================
  Files          95       95              
  Lines       13153    13203      +50     
==========================================
+ Hits         8557     8588      +31     
- Misses       4596     4615      +19

Impacted Files	Coverage Δ
source/tools/Random.h	54.07% <100%> (+1.04%)	⬆️
tests/test_tools.cc	99.36% <100%> (+0.02%)	⬆️
source/hardware/AvidaGP.h	40.28% <0%> (-7.11%)	⬇️
source/hardware/AvidaCPU_InstLib.h	44.11% <0%> (-2.95%)	⬇️
source/hardware/InstLib.h	34.37% <0%> (-1.57%)	⬇️

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[mmore500]

@mercere99 when you have a chance, I think this should be ready to merge

[mercere99]

Straightforward change -- should work well. Tests look good now.