test(core): assert list size before allSatisfy in DTypeIsUnsignedTest (S5841)

allSatisfy passes vacuously on an empty list; assert hasSize(7) first so the
test cannot silently pass if the fixture list is ever emptied.

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

Author: dfa1

core/src/test/java/io/github/dfa1/vortex/core/model/DTypeIsUnsignedTest.java

@@ -33,6 +33,6 @@ void nonPrimitiveTypes_areNotUnsigned() {
                 new DType.Struct(List.of("u"), List.of(DType.U64), false));
 
         // When / Then
-        assertThat(types).allSatisfy(t -> assertThat(t.isUnsigned()).isFalse());
+        assertThat(types).hasSize(7).allSatisfy(t -> assertThat(t.isUnsigned()).isFalse());
     }
 }