Wrong result for MemTableTraverseIterator::GetCount()

When using traverseIterator to traverse Memtable, GetCount() is used to get the traverse count. The meaning of 'traverse count' is not clear. and if we regard it as 'how many pieces of data it has traversed' then the result is not correct.

## Situation
``` cpp
TEST_F(TableTest, TraverseIteratorCount) {
::openmldb::api::TableMeta table_meta;
table_meta.set_name("table1");
table_meta.set_tid(1);
table_meta.set_pid(0);
table_meta.set_seg_cnt(8);
table_meta.set_mode(::openmldb::api::TableMode::kTableLeader);
table_meta.set_key_entry_max_height(8);
table_meta.set_format_version(1);
SchemaCodec::SetColumnDesc(table_meta.add_column_desc(), "card", ::openmldb::type::kString);
SchemaCodec::SetColumnDesc(table_meta.add_column_desc(), "mcc", ::openmldb::type::kString);
SchemaCodec::SetColumnDesc(table_meta.add_column_desc(), "price", ::openmldb::type::kBigInt);
SchemaCodec::SetColumnDesc(table_meta.add_column_desc(), "ts1", ::openmldb::type::kBigInt);
SchemaCodec::SetColumnDesc(table_meta.add_column_desc(), "ts2", ::openmldb::type::kBigInt);
SchemaCodec::SetIndex(table_meta.add_column_key(), "card", "card", "ts1", ::openmldb::type::kAbsoluteTime, 0, 0);
SchemaCodec::SetIndex(table_meta.add_column_key(), "card1", "card", "ts2", ::openmldb::type::kAbsoluteTime, 0, 0);
SchemaCodec::SetIndex(table_meta.add_column_key(), "mcc", "mcc", "ts1", ::openmldb::type::kAbsoluteTime, 0, 0);

MemTable table(table_meta);
table.Init();
codec::SDKCodec codec(table_meta);

for (int i = 0; i < 1000; i++) {
std::vector row = {"card" + std::to_string(i % 100), "mcc" + std::to_string(i),
"13", std::to_string(1000 + i), std::to_string(10000 + i)};
::openmldb::api::PutRequest request;
::openmldb::api::Dimension* dim = request.add_dimensions();
dim->set_idx(0);
dim->set_key(row[0]);
dim = request.add_dimensions();
dim->set_idx(1);
dim->set_key(row[0]);
dim = request.add_dimensions();
dim->set_idx(2);
dim->set_key(row[1]);
std::string value;
ASSERT_EQ(0, codec.EncodeRow(row, &value));
table.Put(0, value, request.dimensions());
}
TableIterator* it = table.NewTraverseIterator(0);
it->SeekToFirst();
int count = 0;
while (it->Valid()) {
count++;
it->Next();
}
ASSERT_EQ(1000, count);
ASSERT_EQ(1100, (int64_t)it->GetCount());
delete it;
}
```

## Expected Behavior

The result of (int64_t)it->GetCount() should probably be 1000

## Current Behavior

It's 1100 as the test says.

## Steps to Reproduce
make and run table_test, in TEST_F(TableTest, TraverseIteratorCount)

The issue is in MemTableTraverseIterator::GetCount() within the OpenMLDB codebase. Start by examining the table_test.cpp file and the specific test case 'TraverseIteratorCount'. Look at the MemTable and MemTableTraverseIterator implementations to understand how the count is incremented. The test inserts 1000 rows but expects GetCount() to return 1000, not 1100. Run the test to reproduce the failure, then trace the logic in GetCount() to identify why it overcounts.

由索引模型根据 Issue 内容生成。