[#213] fix Redis protocol error too big inline request

Redis bulk load commands need to be under 64 KB per line (more or less):

redis/redis-rb#1185

https://github.com/redis/redis/blob/07b292af5e86459e435da5986f87bc4f7415d437/src/server.h#L178

If too many IDs are included in the batch file, the lines are too long,
causing an error:

    ERR Protocol error: too big inline request

Fix by chunking IDs written to lines.

What chunk size to use? 1000 IDs works, and leads to lines of
approximately 23 KB. But Register 2 generates statement IDs of around 20
characters in length, whereas BODS 0.2 and BODS 0.3 says they must be
between 32 and 64 chars (the fact that Register 2 doesn't comply with
the minimum is a separate issue). Multiplying by 20/64 gives a target of
around 20 KB, so reducing to 750 IDs should be comfortable, leading to
lines of around 17 KB (as measured with `wc -c`).

bin/combine

@@ -8,6 +8,7 @@ dst_f=${2:-$dst_f_}
 ns=register-files-combiner
 tmp=$(mktemp -d)
 tmp_redis=$tmp/batch.redis
+chunk_size=750
 #-------------------------------------------------------------------------------
 function _clean() {
     rm -rf "${tmp:?}"
@@ -42,7 +43,10 @@ for src_f in "${src_fs[@]}" ; do
         mapfile -t ids < <(
             jq -r '.statementID' < "$src_f"
         )
-        echo "SADD '$src_k' ${ids[*]@Q}" >> "$tmp_redis"
+        for ((i=0 ; i < ${#ids[@]}; i+=chunk_size)) ; do
+            chunk=( "${ids[@]:i:$chunk_size}" )
+            echo "SADD '$src_k' ${chunk[*]@Q}" >> "$tmp_redis"
+        done
         state='*'
         src_k_n=${#ids[@]}
     else