add a Rust toolchain file

fix the toolchain version of Rust with rust-toolchain.toml.

this is to avoid having things like cargo clippy behaving differently locally and in the remote CI.

Note
see https://gitlab.isae-supaero.fr/dragoon/komodo/-/jobs/12875 which fails with Rust 1.72 but works locally with Rust 1.75

enabled an automatic merge when the pipeline for 39c8fe75 succeeds

aborted the automatic merge because source branch was updated

added 1 commit

• e2e171f2 - bump the rust toolchain in the CI

Compare with previous version

mentioned in issue #6 (closed)

merged

mentioned in commit 9fe62d5a

mentioned in merge request !42 (merged)

mentioned in commit e0fb0f81