cesium/oracle: passes() must not accept -inf PSNR

is_infinite() is true for both +inf and -inf; a -inf PSNR would wrongly
satisfy any minimum-PSNR gate. Only +inf (identical buffers, MSE=0) should
auto-pass. (CodeRabbit, oracle.rs passes().)

https://claude.ai/code/session_017GFLBnDy23AWBqvkbHHC41

Author: claude

crates/cesium/src/oracle.rs

@@ -295,7 +295,7 @@ impl ParityMetrics {
     /// }
     /// ```
     pub fn passes(&self, min_ssim: f32, min_psnr_db: f32) -> bool {
-        self.ssim >= min_ssim && (self.psnr >= min_psnr_db || self.psnr.is_infinite())
+        self.ssim >= min_ssim && (self.psnr >= min_psnr_db || self.psnr == f32::INFINITY)
     }
 }