rtx-cfd legacy GPU: buffers re-borrowed after nested device calls; writing and delegating methods take &mut self

crates/specialized/rtx-cfd/src/solvers/incompressible/simple_gpu.rs

@@ -183,7 +183,7 @@ impl SimpleGpuSolver {
     async fn gpu_momentum_prediction(&mut self, dt: f32) -> CfdResult<()> {
         let buffers = self
             .gpu_buffers
-            .as_ref()
+            .as_mut()
             .ok_or_else(|| CfdError::gpu_error("GPU buffers not initialized"))?;
 
         let config = self.cpu_solver.config();
@@ -250,7 +250,7 @@ impl SimpleGpuSolver {
     async fn gpu_pressure_correction(&mut self) -> CfdResult<f32> {
         let buffers = self
             .gpu_buffers
-            .as_ref()
+            .as_mut()
             .ok_or_else(|| CfdError::gpu_error("GPU buffers not initialized"))?;
 
         let config = self.cpu_solver.config();
@@ -297,10 +297,10 @@ impl SimpleGpuSolver {
     }
 
     /// GPU-accelerated pressure update step
-    async fn gpu_pressure_update(&self, pressure_relaxation: f32) -> CfdResult<()> {
+    async fn gpu_pressure_update(&mut self, pressure_relaxation: f32) -> CfdResult<()> {
         let buffers = self
             .gpu_buffers
-            .as_ref()
+            .as_mut()
             .ok_or_else(|| CfdError::gpu_error("GPU buffers not initialized"))?;
 
         // p = p + α_p * p'  (pressure update with relaxation)