CBOR: carry ice_ring_score in the END block

The per-image ice ring score was encoded for every DataMessage but never
for the END message, although docs/CBOR.md has always listed it there and
both NXmx::EndResultVectors and HDF5MetadataSource expect it. Any dataset
written over the stream therefore had no /entry/MX/iceRingScore, and under
NXmxIntegrated - where the whole-run vector is the only copy - the score
was lost entirely.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

frame_serialize/CBORStream2Serializer.cpp

@@ -773,6 +773,7 @@ void CBORStream2Serializer::SerializeSequenceEnd(const EndMessage& message) {
     CBOR_ENC(mapEncoder, "spot_count_indexed", message.spot_count_indexed);
     CBOR_ENC(mapEncoder, "image_indexed", message.image_indexed);
     CBOR_ENC(mapEncoder, "v_bkg_estimate", message.v_bkg_estimate);
+    CBOR_ENC(mapEncoder, "ice_ring_score", message.ice_ring_score);
     CBOR_ENC(mapEncoder, "profile_radius", message.profile_radius);
     CBOR_ENC(mapEncoder, "mosaicity", message.mosaicity);
     CBOR_ENC(mapEncoder, "bFactor", message.bFactor);