Improve lmms::fastRand() and use it instead of std::rand()

[rubiefawn]

• Combine overloads of lmms::fastRand() into one template
  • Remove RAND_MAX constant since it is not used outside lmms::fastRand() (and all places that did previously use it should have been calling lmms::fastRand() anyway)
  • This is also done to lmms::fastLog10f() for consistency, though it is not related to the goal of the PR
• Add lmms::oneIn() convenience function to replace occurences of (fastRand() % chance == 0)
• Replace uses of std::rand() with lmms::fastRand() for consistency
• Replace uses of scale * lmms::fastRand() / RAND_MAX - offset with lmms::fastRand(min, max)

// Old
int x = static_cast<int>(10.0f * rand() / RAND_MAX - 3.0f);

// New
int x = fastRand(-3, 7);

Testing

• [x] Triple Oscillator noise sounds the same
• [x] Organic randomize preset button works
• [x] Multiple Peak Controllers can coexist
• [x] Sfxr randomize preset button works
• [x] SID plugin sounds the same
• [x] Vibed plugin sounds the same
• [x] .ds samples with noise sound the same
• [x] Undo/redo doesn't instantly explode
• [x] Mixer channel color randomization works
• [x] Clip color randomization works
• [x] Track color randomization works

[bratpeki]

Briefly tested Mallets, Spectrum Analyzer, ReverbSC, Flanger and Ogranic. I think we can (finally) merge! :tada:

[rubiefawn]

Now that this has an approval from a dev with write access, I plan to merge this PR on 2026-01-08, provided no issues are found in the meantime. If anyone else would like to review this PR, please do so before that date.