Make memory.ts use Buffers instead of Arrays

[ryanio]

This PR closes #827.

[codecov]

Codecov Report

Merging #850 into master will decrease coverage by 0.03%.
The diff coverage is 100.00%.

Flag	Coverage Δ
#account	92.85% <ø> (ø)
#block	77.81% <ø> (-0.26%)	⬇️
#blockchain	81.33% <ø> (ø)
#common	94.14% <ø> (ø)
#ethash	82.22% <ø> (ø)
#tx	94.02% <ø> (-0.14%)	⬇️
#vm	92.49% <100.00%> (ø)

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[holgerd77]

Ok, first was confused that there are SO few code changes necessary, but then I did some manual tests on the console e.g. for the write() logic, wasn't aware that arrays and Buffers behave so similarly. So looks good.

Speed change is not really apparent, might nevertheless be a small improvement not measurable by the benchmarks. Will merge.

[alcuadrado]

I love the new benchmarking action and this kind of prs! 😍

As Holger mentioned, the performance change is not clear, but it may be because of the benchmarks being too general. Still, having them will be useful to compare things in the mid-term, at least.