Upgrade workspace to Rust 1.94.0

[alamb]

Is your feature request related to a problem or challenge?

Rist 1.94 was released recently: https://blog.rust-lang.org/2026/03/05/Rust-1.94.0/

Describe the solution you'd like

let's update our workspace to use it.

Describe alternatives you've considered

The toolchain is defined https://github.com/apache/datafusion/blob/main/rust-toolchain.toml

You can follow @dariocurr 's pattern here to update

• build: update Rust toolchain version from 1.92.0 to 1.93.0 in rust-toolchain.toml #20309

Note that it is important to run clippy and cargo_fmt before submitting a PR

Additional context

No response