Add missing headers

[rupprecht]

When using libc++ after llvm/llvm-project@ada3786, #include <random> does not imply #include <cmath>, so we need to directly import it to avoid breakages, e.g.

faiss/utils/random.cpp:140:40: error: use of undeclared identifier 'log'; did you mean 'long'?
  140 |                 x[i] = a * sqrt(-2.0 * log(s) / s);

While #include <cmath> is the only one necessary to fix a breakage from that LLVM commit, there are a few other C++ headers not being directly included, so I included those to prevent future breakages from refactorings.

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