test: add 64 MiB (cache-busting) payload to benchmarks

Exercises the DRAM-bandwidth-bound regime past L3, where the zero-copy
MemorySegment edge collapses to parity with byte[]/JNI.

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

Author: dfa1

benchmark/src/main/java/io/github/dfa1/zstdffm/bench/CompressBenchmark.java

@@ -35,7 +35,7 @@
 @Measurement(iterations = 5)
 public class CompressBenchmark {
 
-    @Param({"1024", "65536", "1048576"})
+    @Param({"1024", "65536", "1048576", "67108864"})
     private int size;
 
     @Param({"3"})

benchmark/src/main/java/io/github/dfa1/zstdffm/bench/DecompressBenchmark.java

@@ -35,7 +35,7 @@
 @Measurement(iterations = 5)
 public class DecompressBenchmark {
 
-    @Param({"1024", "65536", "1048576"})
+    @Param({"1024", "65536", "1048576", "67108864"})
     private int size;
 
     private int originalSize;