Compileable in both Stable and Nightly Rust

[alexniver]

may be stable rust is better?

[victorb]

I've added Rust Stable as a CI target, so now we at least attempt to test both Stable and Nightly.

However, I'm using the bench feature which isn't available in Stable, so the benchmark kind of require Nightly. Didn't figure out how to skip that for Stable in the ~5 minutes I had available, so reopening this issue until I (or someone else) figured out how to skip that file for Rust Stable but not Nightly.

error[E0554]: `#![feature]` may not be used on the stable release channel
 --> crates/dogoap/benches/long_plan.rs:1:1
  |
1 | #![feature(test)]
  | ^^^^^^^^^^^^^^^^^

For more information about this error, try `rustc --explain E0554`.