fix: restore MaskedArray.segment() delegation to inner array

Removed buffer(0) delegation when dropping Array interface methods;
segment() on MaskedArray now throws, breaking AlpEncoding, ChunkedEncoding,
and RunEndEncoding when decoding nullable columns. Restore delegation via
deprecated segment() override on MaskedArray and unwrap in ScanIterator.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: dfa1

core/src/main/java/io/github/dfa1/vortex/core/array/MaskedArray.java

@@ -2,6 +2,8 @@
 
 import io.github.dfa1.vortex.core.DType;
 
+import java.lang.foreign.MemorySegment;
+
 /// Decoded {@code vortex.masked} array: a non-nullable child paired with an optional validity bitmap.
 ///
 /// <p>Invariant: {@code child} has no actual nulls — nullability is expressed solely via
@@ -40,6 +42,17 @@ public Array inner() {
         return child;
     }
 
+    /// Delegates to {@link #inner()}'s segment; validity is not surfaced here.
+    ///
+    /// @return the primary segment of the inner array
+    /// @deprecated inherited from {@link Array#segment()}; validity silently dropped — prefer {@link #inner()} directly
+    @Override
+    @Deprecated(forRemoval = true)
+    @SuppressWarnings("deprecation")
+    public MemorySegment segment() {
+        return child.segment();
+    }
+
     /// Returns the validity bitmap, or {@code null} if all positions are valid.
     ///
     /// @return the validity bitmap, or {@code null} when all values are valid

reader/src/main/java/io/github/dfa1/vortex/scan/ScanIterator.java

@@ -388,7 +388,8 @@ private Array decodeConcatPrimitive(List<Layout> flats, DType dtype, long totalR
         long byteOffset = 0;
         for (Layout flat : flats) {
             Array chunk = decodeFlat(flat, dtype, arena);
-            MemorySegment src = chunk.segment();
+            Array chunkData = chunk instanceof MaskedArray m ? m.inner() : chunk;
+            MemorySegment src = chunkData.segment();
             MemorySegment.copy(src, 0, combined, byteOffset, src.byteSize());
             byteOffset += src.byteSize();
         }