style(hpc): rustfmt — collapse multi-line assert in heel_f64x8 linf test

CI `format/stable` job flagged `cargo fmt --check` diff: the new
`linf_picks_the_largest_gap` test (commit 71cdbd4) had a multi-line
`assert!(...)` invocation. rustfmt prefers it on one line. Auto-applied
via `cargo fmt`.

No code change. CI signal: PR #160 format/stable.

Author: claude

src/hpc/heel_f64x8.rs

@@ -343,11 +343,7 @@ mod l1_l2_linf_tests {
         let a = vec![0.0f64, 0.0, 5.0, 0.0];
         let b = vec![0.0f64, 0.0, 0.0, 0.0];
         let result = linf_f64_simd(&a, &b);
-        assert!(
-            (result - 5.0).abs() < f64::EPSILON,
-            "L∞ should be 5.0, got {}",
-            result
-        );
+        assert!((result - 5.0).abs() < f64::EPSILON, "L∞ should be 5.0, got {}", result);
     }
 }