feat(rsjudge-runner): 🚩 add setgroups flag, allow using groups method…

… from std

crates/rsjudge-runner/Cargo.toml

@@ -13,3 +13,6 @@ caps = "0.5.5"
 nix = { version = "0.28.0", features = ["user"] }
 once_cell = "1.19.0"
 uzers = "0.11.3"
+
+[features]
+setgroups = []

crates/rsjudge-runner/src/lib.rs

@@ -26,12 +26,17 @@ impl RunAs for Command {
         // and no longer accessible outside it.
         //
         // Replace with `CommandExt::groups` once it's stable.
+        #[cfg(not(feature = "setgroups"))]
         unsafe {
             self.pre_exec(move || {
                 setgroups(&groups)?;
                 Ok(())
             })
         };
+
+        #[cfg(feature = "setgroups")]
+        self.groups(groups);
+
         self
     }
 }