Add more examples of runtime dimensions to examples/02-ops.rs

[coreylowman]

Currently examples/01-tensor.rs shows how to create tensors with runtime dimensions, but there are no corresponding examples in 02-ops.rs.

1. Add some of the tensors in examples/02-tensor to use both runtime & const dimensions.
2. Change the first matmul call to use both runtime & const dims
3. Show an example of using RealizeTo trait to add tensors with different types of dimensions:

let a: Tensor<(Const<3>, usize), f32, _> = dev.sample_uniform_like(&(Const, 5));
let b: Tensor<(usize, Const<5>), f32, _> = dev.sample_uniform_like(&(3, Const));
let c = a + b.realize().unwrap();