Function dispatch_dot_f64 

pub fn dispatch_dot_f64(a: &[f64], b: &[f64], ctx: &ReductionContext) -> f64

Dot product of two equal-length f64 slices using dispatched summation.

Computes element-wise products, then sums with the selected strategy. For Binned strategy, the products Vec is collected on the stack (via Vec) before passing to the accumulator. This is acceptable because the Vec is for the products array, not the accumulator itself.