Add power compute kernel

**Is your feature request related to a problem or challenge? Please describe what you are trying to do.**
We are working on adding a `power` function / operator to datafusion (https://github.com/apache/arrow-datafusion/issues/1493). Rather than implementing in datafusion i propose adding it as a compute kernel in arrow because we can implement directly with rust float primitives (https://doc.rust-lang.org/std/primitive.u32.html#method.pow, https://doc.rust-lang.org/std/primitive.f32.html#method.powf, etc) without any additional logic, similar to existing arrow compute kernels, and this aligns with the C++ compute implementation (https://arrow.apache.org/docs/cpp/compute.html#arithmetic-functions) and arrow2 (https://github.com/jorgecarleitao/arrow2/blob/main/src/compute/arithmetics/basic/pow.rs)

**Describe the solution you'd like**
`power` (using two arrays) and `power_scalar` (array and scalar) compute kernels

**Describe alternatives you've considered**
A clear and concise description of any alternative solutions or features you've considered.

**Additional context**
Add any other context or screenshots about the feature request here.

Start by examining the existing Arrow Rust compute kernels and the linked Rust primitive methods, then compare the C++ arithmetic functions and arrow2 power implementation referenced in the issue. Done means providing the requested power and power_scalar kernels for array and scalar inputs, with behavior aligned with the surrounding compute APIs.

Written by the indexing model from the issue text.