Upgrade toolchain to Rust 1.86

[alamb]

Is your feature request related to a problem or challenge?

Rust 1.86 was released last week https://blog.rust-lang.org/2025/04/03/Rust-1.86.0.html

We should update DataFusion to use the latest rust, among other things to get improved build time as @logan-keede has observed improvements in #13814 (comment)

Describe the solution you'd like

Follow the instructions here about how to upgrade

datafusion/docs/source/contributor-guide/howtos.md

Line 22 in 8a6e98d

## How to update the version of Rust used in CI tests

Describe alternatives you've considered

No response

Additional context

No response

[alamb]

I think instructions for this are pretty clear and this should be largely mechanical

recommendations for anyone taking this one on:

1. Run clippy locally
2. Run the compiler locally to fix warnings

Once you get clippy to run I suspect everything else will "just work"

[jsai28]

take