Fix broken slice_scatter example in basics.rs

[davenpi]

Problem

The basics.rs example in candle-core/examples fails to run due to a shape mismatch error:

$ cargo run --example basics -p candle-core
Error: shape mismatch in slice-scatter (self, src), lhs: [3, 2], rhs: [2, 1]

because

let a = Tensor::new(&[[0.0f32, 1.0, 2.0], [3.0, 4.0, 5.0]], &Device::Cpu)?;  // [2, 3]
let b = Tensor::new(&[[88.0f32, 99.0]], &Device::Cpu)?;                      // [1, 2] ❌
let new_a = a.slice_scatter(&b, 1, 2)?;  // Trying to scatter into column 2

Fix

// Before
let b = Tensor::new(&[[88.0f32, 99.0]], &Device::Cpu)?;  // [1, 2] row vector

// After  
let b = Tensor::new(&[[88.0f32], [99.0]], &Device::Cpu)?;  // [2, 1] column vector

Also updated the assertion to match the expected result after column replacement.

[ivarflakstad]

Thanks :)