Add EIGENRAND_BUILD_BENCHMARK cmake option

[jorisv]

Hello @bab2min,

Here a PR to turn benchmark building optional.
Today, when using EigenRand as a submodule or with FetchContent, EigenRand benchmark are added to the main project test.
With this PR, we can disable them, and avoid running it.

Thanks !

[ManifoldFR]

Seems there's an #include <cstdio> missing and the build step actually fails (but the CI reports a success) @bab2min

[jorisv]

Hello @bab2min,

All the checks are green except the one on Windows avx512.
I think the Windows agent doesn't support avx512 and then can't run the unit test.

[bab2min]

@jorisv Yes, I think so. It seems to be an error in the CPU running unit test, not an error in the code.
Looks good to me. Thank you for your useful and meaningful contribution.
@ManifoldFR

[ManifoldFR]

Thank you @bab2min !

I didn't forget my issue #53 on adding PDFs/CDFs to the library, sadly I've been sidetracked the past few months so I don't have a PR for that yet but I hope to clear time for that soon.