fix(reader): restore long cast in Pco preDeltaN clamp (S2184)

Removing the (long) cast in 04cab70 turned `nRemaining - deltaOrder`
into an int subtraction widened only afterward for Math.clamp(long,..),
risking int overflow — SonarCloud flagged it as bug S2184. The cast was
load-bearing, not redundant as S1905 claimed; restore it.

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

Author: dfa1

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

@@ -290,8 +290,8 @@ private static void decodeIntMultPage(
 
         while (nRemaining > 0) {
             int batchN = Math.min(nRemaining, PcoTansDecoder.BATCH_N);
-            int primaryPreDeltaN = (int) Math.clamp(nRemaining - deltaOrder, 0, batchN);
-            int secondaryPreDeltaN = (int) Math.clamp(nRemaining - secondaryDeltaOrder, 0, batchN);
+            int primaryPreDeltaN = (int) Math.clamp((long) nRemaining - deltaOrder, 0, batchN);
+            int secondaryPreDeltaN = (int) Math.clamp((long) nRemaining - secondaryDeltaOrder, 0, batchN);
 
             primaryTans.decodeBatch(pageReader, primaryStateIdxs, primaryPreDeltaN,
                     batchLowersP, batchOffsetBitsP, rawMults, primaryPos);