fix(writer): clear two Sonar bugs in the SUM stat plumbing

- scalarDouble: branch instead of a ternary so the F32 path widens
  Float -> double explicitly rather than mixing boxed Double/Float
  operands (java:S2154).
- ChunkRef: suppress java:S6218 — the byte[] stat components are never
  value-compared (instances live in per-column lists, read positionally),
  so the default identity equals is correct and an override would be dead
  code.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: dfa1

writer/src/main/java/io/github/dfa1/vortex/writer/VortexWriter.java

@@ -974,9 +974,13 @@ private static long scalarLong(byte[] bytes) throws IOException {
     }
 
     private static double scalarDouble(byte[] bytes) throws IOException {
-        // Float columns serialise min/max as f64 (F64) or f32 (F32).
+        // Float columns serialise min/max as f64 (F64) or f32 (F32). Branch rather than use a
+        // ternary so the F32 path widens Float -> double explicitly instead of mixing boxed types.
         ScalarValue sv = decodeScalar(bytes);
-        return sv.f64_value() != null ? sv.f64_value() : sv.f32_value();
+        if (sv.f64_value() != null) {
+            return sv.f64_value();
+        }
+        return sv.f32_value();
     }
 
     private static ScalarValue decodeScalar(byte[] bytes) throws IOException {
@@ -1432,6 +1436,9 @@ private static Object buildCodesArray(Object data, PType ptype, Map<Object, Inte
     private record SegRef(long offset, long len) {
     }
 
+    // S6218: the byte[] stat components are never value-compared — ChunkRef instances are only
+    // collected in per-column lists and read positionally, so the default identity equals is fine.
+    @SuppressWarnings("java:S6218")
     private record ChunkRef(int segIdx, long rowCount, byte[] statsMin, byte[] statsMax,
             byte[] statsSum, long nullCount) {
         boolean hasStats() {