refactor(decode): drop unused accepts(DType) from EncodingDecoder SPI

accepts(DType) was a residual of the ADR-0001 read/write runtime split: the
pre-split unified Encoding interface combined encode + accepts + decode, and
the split copied the full method set onto both EncodingDecoder and
EncodingEncoder. accepts is encode-selection semantics ("can this encoding
*encode* the dtype") — the writer's CascadingCompressor and friends still use
EncodingEncoder.accepts, but the reader dispatches decoders purely by
EncodingId (ReadRegistry's Map<EncodingId, EncodingDecoder>) and never calls
it. The method has been dead on the read side since the split; SonarCloud
flagged it as uncovered on BitpackedEncodingDecoder.

Remove accepts from the EncodingDecoder interface and all 33 implementations,
plus the decoder-side accepts assertions in the unit tests (the writer
encoder.accepts assertions stay). Added a DictEncodingDecoderTest#encodingId
test to keep that outer class from collapsing to a checkstyle utility class
once its only non-nested test was removed.

EncodingEncoder.accepts is unchanged.

Verified: full unit suite (all modules) green; reader/writer build clean
(javac -Werror, checkstyle, javadoc).

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

Author: dfa1

reader/src/main/java/io/github/dfa1/vortex/reader/decode/AlpEncodingDecoder.java

@@ -38,14 +38,6 @@ public EncodingId encodingId() {
         return EncodingId.VORTEX_ALP;
     }
 
-    @Override
-    public boolean accepts(DType dtype) {
-        if (!(dtype instanceof DType.Primitive p)) {
-            return false;
-        }
-        return p.ptype() == PType.F64 || p.ptype() == PType.F32;
-    }
-
     @Override
     public Array decode(DecodeContext ctx) {
         ByteBuffer rawMeta = ctx.metadata();

reader/src/main/java/io/github/dfa1/vortex/reader/decode/AlpRdEncodingDecoder.java

@@ -34,14 +34,6 @@ public EncodingId encodingId() {
         return EncodingId.VORTEX_ALPRD;
     }
 
-    @Override
-    public boolean accepts(DType dtype) {
-        if (!(dtype instanceof DType.Primitive p)) {
-            return false;
-        }
-        return p.ptype() == PType.F32 || p.ptype() == PType.F64;
-    }
-
     @Override
     public Array decode(DecodeContext ctx) {
         ALPRDMetadata meta = parseMeta(ctx);

reader/src/main/java/io/github/dfa1/vortex/reader/decode/BitpackedEncodingDecoder.java

@@ -31,17 +31,6 @@ public EncodingId encodingId() {
         return EncodingId.FASTLANES_BITPACKED;
     }
 
-    @Override
-    public boolean accepts(DType dtype) {
-        if (!(dtype instanceof DType.Primitive p)) {
-            return false;
-        }
-        return switch (p.ptype()) {
-            case I8, I16, I32, I64, U8, U16, U32, U64 -> true;
-            default -> false;
-        };
-    }
-
     @Override
     public Array decode(DecodeContext ctx) {
         ByteBuffer rawMeta = ctx.metadata();

reader/src/main/java/io/github/dfa1/vortex/reader/decode/BoolEncodingDecoder.java

@@ -1,6 +1,5 @@
 package io.github.dfa1.vortex.reader.decode;
 
-import io.github.dfa1.vortex.core.DType;
 import io.github.dfa1.vortex.encoding.EncodingId;
 import io.github.dfa1.vortex.reader.array.Array;
 import io.github.dfa1.vortex.reader.array.MaterializedBoolArray;
@@ -19,11 +18,6 @@ public EncodingId encodingId() {
         return EncodingId.VORTEX_BOOL;
     }
 
-    @Override
-    public boolean accepts(DType dtype) {
-        return dtype instanceof DType.Bool;
-    }
-
     @Override
     public Array decode(DecodeContext ctx) {
         return new MaterializedBoolArray(ctx.dtype(), ctx.rowCount(), ctx.buffer(0));

reader/src/main/java/io/github/dfa1/vortex/reader/decode/ByteBoolEncodingDecoder.java

@@ -1,6 +1,5 @@
 package io.github.dfa1.vortex.reader.decode;
 
-import io.github.dfa1.vortex.core.DType;
 import io.github.dfa1.vortex.encoding.EncodingId;
 import io.github.dfa1.vortex.reader.array.Array;
 import io.github.dfa1.vortex.reader.array.MaterializedBoolArray;
@@ -21,11 +20,6 @@ public EncodingId encodingId() {
         return EncodingId.VORTEX_BYTEBOOL;
     }
 
-    @Override
-    public boolean accepts(DType dtype) {
-        return dtype instanceof DType.Bool;
-    }
-
     @Override
     public Array decode(DecodeContext ctx) {
         long n = ctx.rowCount();

reader/src/main/java/io/github/dfa1/vortex/reader/decode/ChunkedEncodingDecoder.java

@@ -35,13 +35,6 @@ public EncodingId encodingId() {
         return EncodingId.VORTEX_CHUNKED;
     }
 
-    @Override
-    public boolean accepts(DType dtype) {
-        return dtype instanceof DType.Primitive
-                || dtype instanceof DType.Bool
-                || dtype instanceof DType.Struct;
-    }
-
     @Override
     public Array decode(DecodeContext ctx) {
         int nchildren = ctx.node().children().length;

reader/src/main/java/io/github/dfa1/vortex/reader/decode/ConstantEncodingDecoder.java

@@ -35,11 +35,6 @@ public EncodingId encodingId() {
         return EncodingId.VORTEX_CONSTANT;
     }
 
-    @Override
-    public boolean accepts(DType dtype) {
-        return dtype instanceof DType.Primitive;
-    }
-
     @Override
     public Array decode(DecodeContext ctx) {
         MemorySegment scalarBuf = ctx.buffer(0);

reader/src/main/java/io/github/dfa1/vortex/reader/decode/DateTimePartsEncodingDecoder.java

@@ -33,11 +33,6 @@ public EncodingId encodingId() {
         return EncodingId.VORTEX_DATETIMEPARTS;
     }
 
-    @Override
-    public boolean accepts(DType dtype) {
-        return dtype instanceof DType.Extension;
-    }
-
     @Override
     public Array decode(DecodeContext ctx) {
         ByteBuffer meta = ctx.metadata();

reader/src/main/java/io/github/dfa1/vortex/reader/decode/DecimalBytePartsEncodingDecoder.java

@@ -24,11 +24,6 @@ public EncodingId encodingId() {
         return EncodingId.VORTEX_DECIMAL_BYTE_PARTS;
     }
 
-    @Override
-    public boolean accepts(DType dtype) {
-        return dtype instanceof DType.Decimal;
-    }
-
     @Override
     public Array decode(DecodeContext ctx) {
         ByteBuffer meta = ctx.metadata();

reader/src/main/java/io/github/dfa1/vortex/reader/decode/DecimalEncodingDecoder.java

@@ -1,6 +1,5 @@
 package io.github.dfa1.vortex.reader.decode;
 
-import io.github.dfa1.vortex.core.DType;
 import io.github.dfa1.vortex.core.VortexException;
 import io.github.dfa1.vortex.reader.array.Array;
 import io.github.dfa1.vortex.reader.array.LazyDecimalArray;
@@ -23,11 +22,6 @@ public EncodingId encodingId() {
         return EncodingId.VORTEX_DECIMAL;
     }
 
-    @Override
-    public boolean accepts(DType dtype) {
-        return dtype instanceof DType.Decimal;
-    }
-
     @Override
     public Array decode(DecodeContext ctx) {
         ByteBuffer meta = ctx.metadata();