[opt](mow) opt mow lookup with sequence column (apache#38287)

Compare primary key without sequence column is expensive,
if full key is exact_match, the primary key without sequence column
should also the same,
do not need to compare again.

be/src/olap/rowset/segment_v2/segment_iterator.cpp

@@ -1388,7 +1388,7 @@ Status SegmentIterator::_lookup_ordinal_from_pk_index(const RowCursor& key, bool
 
     // The sequence column needs to be removed from primary key index when comparing key
     bool has_seq_col = _segment->_tablet_schema->has_sequence_col();
-    if (has_seq_col) {
+    if (has_seq_col && !exact_match) {
         size_t seq_col_length =
                 _segment->_tablet_schema->column(_segment->_tablet_schema->sequence_col_idx())
                         .length() +