refactor: improve code quality and remove unused imports

- Use if-let pattern for cleaner option handling in direct_solver
- Remove unused imports from window wgpu tests

Author: farhan-syah

src/integrate/impl_generic/ode/direct_solver.rs

@@ -193,10 +193,8 @@ impl<R: Runtime> DirectSparseSolver<R> {
         // Apply equilibration to cached CSC if enabled
         let factored_csc = if self.equilibrate {
             let csc_ref = self.cached_permuted_csc.as_ref().unwrap();
-            if self.row_scales.is_some() {
+            if let (Some(row_scales), Some(col_scales)) = (&self.row_scales, &self.col_scales) {
                 // Reuse cached scales
-                let row_scales = self.row_scales.as_ref().unwrap();
-                let col_scales = self.col_scales.as_ref().unwrap();
                 let scaled = csc_ref.scale_rows(row_scales)?;
                 scaled.scale_cols(col_scales)?
             } else {

src/window/wgpu/window.rs

@@ -104,9 +104,6 @@ impl WindowFunctions<WgpuRuntime> for WgpuClient {
 
 #[cfg(test)]
 mod tests {
-    use super::*;
-    use numr::dtype::DType;
-
     #[test]
     #[ignore] // WebGPU tests require GPU
     fn test_hann_window_wgpu() {