Update rust version to 1.85.0

[avinassh]

The CI is failing with following error:

installing nextest
    Updating crates.io index
error: cannot install package `cargo-nextest 0.9.97`, it requires rustc 1.85 or newer, while the currently active rustc version is 1.82.0
`cargo-nextest 0.9.97-b.2` supports rustc 1.81
non 0 exit code: exit status: 101
Error: Process completed with exit code 255.

https://github.com/tursodatabase/libsql/actions/runs/15376592072/job/43262042664

So this patch updates the rust version

[Copilot]

Pull Request Overview

This PR updates the Rust toolchain version to 1.85.0 to address CI failures with the cargo-nextest dependency.

• Updated channel from "1.82.0" to "1.85.0" in rust-toolchain.toml