Finish DS4 execution parity

src/settings.rs

@@ -351,8 +351,12 @@ impl DiagnosticPreferences {
         if let Some(gib) = self.simulated_used_memory_gib {
             validate_gib("Simulated used memory", gib)?;
         }
-        if self.expert_profile_path.is_some() {
-            return Err("Expert profiling is not available in the Rust Metal executor yet.".into());
+        if self
+            .expert_profile_path
+            .as_deref()
+            .is_some_and(|path| path.trim().is_empty())
+        {
+            return Err("Expert profile path cannot be empty.".into());
         }
         Ok(())
     }