Implement secure_random()

[lovvik]

as asked by issue #683

• Implemented secure_random()
• Added 2 build directories
• Changed calls of fast_random() in src, tests and benchmarks
• Added -lcrypto linking

[gavv]

Thanks for PR!

Regarding my comment from matrix that you linked above: https://github.com/roc-streaming/roc-toolkit/issues/683#issuecomment-2148359306

I guess I was not very clear.

The idea is:

• fast_random is always available and has a single cross-platform implementation; it's not affected by this task at all
• secure_random is always available
• but secure_random can have two different implementations: using OpenSSL, and fallback using fast_random (which as you remember is always available)
• some parts of the code use fast_random, some use secure_random, depending on requirements; CSPRNG is needed when RTP RFC mandates it; but it's slower and can fail, so it's not used everywhere
• regarding tests:
  • we need tests for fast_random and for secure_random; they're different tests at least because these functions have different signatures
  • tests for fast_random should be be affected by this task at all
  • tests for secure_random can have only one implementation, no matter if secure_random is implemented via OpenSSL or fast_random

That's what I tried to say in that comment, we don't need two separate implementations of tests for secure_random, however we still need separate tests for fast_random and secure_random.

[lovvik]

oh...i really misinterpreted it all. It will be fixed.

[github-actions[bot]]

:robot: The latest upstream change made this pull request unmergeable. Please resolve the merge conflicts.