test: use dedicated AssertJ assertions (Sonar S5838)

Replace size/toString/hashCode/map/array equality checks with hasSize,
hasToString, hasSameHashCodeAs, containsEntry, hasSameSizeAs, isNotEmpty.

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

Author: dfa1

core/src/test/java/io/github/dfa1/vortex/encoding/EncodingIdTest.java

@@ -40,7 +40,7 @@ void id_isNonBlankString(EncodingId id) {
         @EnumSource(EncodingId.class)
         void toString_equalsId(EncodingId id) {
             // Given / When / Then
-            assertThat(id.toString()).isEqualTo(id.id());
+            assertThat(id).hasToString(id.id());
         }
     }
 }

core/src/test/java/io/github/dfa1/vortex/proto/ProtoRuntimeTest.java

@@ -316,7 +316,7 @@ void recordsWithEqualByteArraysAreEqual() {
 
             // When + Then
             assertThat(a).isEqualTo(b);
-            assertThat(a.hashCode()).isEqualTo(b.hashCode());
+            assertThat(a).hasSameHashCodeAs(b);
         }
 
         @Test

integration/src/test/java/io/github/dfa1/vortex/integration/RustJavaReaderComparisonIntegrationTest.java

@@ -428,9 +428,9 @@ void rust_vs_javaReader_statsMatch(String fixture, @TempDir Path tmp) throws Exc
                     .as("string column names in %s", fixture)
                     .containsAll(resultRust.strLenSums().keySet());
             for (Map.Entry<String, Long> entry : resultRust.strLenSums().entrySet()) {
-                assertThat(resultJava.strLenSums().get(entry.getKey()))
+                assertThat(resultJava.strLenSums())
                         .describedAs("string column '%s' byte-length sum in %s", entry.getKey(), fixture)
-                        .isEqualTo(entry.getValue());
+                        .containsEntry(entry.getKey(), entry.getValue());
             }
         }
     }

integration/src/test/java/io/github/dfa1/vortex/integration/RustWritesJavaReadsIntegrationTest.java

@@ -549,7 +549,7 @@ void jniWriter_javaReader_f16_primitiveRoundTrip(@TempDir Path tmp) throws IOExc
             assertThat(results).hasSize(1);
             // F16 column snapshots as a short[] (raw float16 bits)
             short[] decoded = (short[]) results.getFirst().columns().get("v");
-            assertThat(decoded.length).isEqualTo(f16bits.length);
+            assertThat(decoded).hasSameSizeAs(f16bits);
             for (int i = 0; i < f16bits.length; i++) {
                 assertThat(Float.float16ToFloat(decoded[i]))
                         .as("index %d", i)

reader/src/test/java/io/github/dfa1/vortex/reader/array/VarBinViewModeTest.java

@@ -60,7 +60,7 @@ void getStringFromReferencedDataBuffer() {
             try (Arena arena = Arena.ofConfined()) {
                 // Given a 13-byte string (exceeds 12-byte inline limit) stored in a shared data buffer.
                 String longStr = "thirteen-byte";
-                assertThat(longStr.length()).isEqualTo(13);
+                assertThat(longStr).hasSize(13);
                 MemorySegment dataBuf = arena.allocate(longStr.length());
                 MemorySegment.copy(MemorySegment.ofArray(longStr.getBytes(StandardCharsets.UTF_8)),
                         0, dataBuf, 0, longStr.length());

writer/src/test/java/io/github/dfa1/vortex/writer/encode/ZstdEncodingEncoderTest.java

@@ -283,7 +283,7 @@ void encode_i32_metadata_framesCount_isNonZero() throws Exception {
             var metaSeg = java.lang.foreign.MemorySegment.ofBuffer(result.rootNode().metadata().duplicate());
             ZstdMetadata meta = ZstdMetadata.decode(metaSeg, 0, metaSeg.byteSize());
 
-            assertThat(meta.frames().size()).isGreaterThan(0);
+            assertThat(meta.frames()).isNotEmpty();
         }
     }
 }