[jdata4] _ArrayChunks_ always stored as array (was scalar for 1-D case)

Spec requires a 1-D integer array; storing a scalar failed schema
validation for the unchunked 1-D case.  Change chunklen → [chunklen]
so the JSON output is always [...] regardless of chunking dimension.
Decoder already used numel()==1 so no decoder change needed.

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

Author: fangq

jdataencode.m

@@ -508,7 +508,7 @@
                     zipchunks{ci} = char(base64encode(zipchunks{ci}));
                 end
             end
-            newitem.(opt.N_ArrayChunks) = chunklen;
+            newitem.(opt.N_ArrayChunks) = [chunklen];
             newitem.(opt.N_ArrayZipSize) = nelem;
             newitem.(opt.N_ArrayZipData) = zipchunks;
         else