Fix irregular_strides benchmark shape type

[wrmsr]

Proposed changes

#2454 changed shapes to SmallVector which broke this benchmark:

/Users/spinlock/src/ml-explore/mlx/benchmarks/cpp/irregular_strides.cpp:79:12: error: no matching function for call to 'uniform'
   79 |   auto a = mx::random::uniform(shape);
      |            ^~~~~~~~~~~~~~~~~~~
/Users/spinlock/src/ml-explore/mlx/mlx/random.h:88:14: note: candidate function not viable: no known conversion from 'std::vector<int>' to 'const Shape' (aka 'const SmallVector<int>') for 1st argument
   88 | inline array uniform(
      |              ^
   89 |     const Shape& shape,
      |     ~~~~~~~~~~~~~~~~~~

I saw #2493 added some std::vector interop but it also says shapes are always SmallVectors.

Would auto shape = mx::Shape{...}; be preferred?

Checklist

Put an x in the boxes that apply.

• I have read the CONTRIBUTING document
• I have run pre-commit run --all-files to format my code / installed pre-commit prior to committing changes
• I have added tests that prove my fix is effective or that my feature works
• I have updated the necessary documentation (if needed)

[awni]

Thanks for fixing that!