Fix clippy int_plus_one warning in ringkernel-wavesim

Change `x + 8 <= width - 1` to equivalent `x + 8 < width`.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: mivertowski

crates/ringkernel-wavesim/src/simulation/grid.rs

@@ -243,7 +243,7 @@ impl SimulationGrid {
         let two = f32x8::splat(2.0);
 
         let mut x = 1;
-        while x + 8 <= width - 1 {
+        while x + 8 < width {
             let idx = row_start + x;
             let local_idx = x;