[Fix](variance) Fix sample variance/stddev NaN res for single value (#63605)

Problem Summary:

Fix `VAR_SAMP`, `VARIANCE_SAMP`, and `STDDEV_SAMP` to return `NaN` when
the number of valid input values is less than or equal to 1. Sample
variance/stddev are undefined for `n <= 1`, so returning `0.0` is
misleading.

before:
```sql
CREATE TABLE t (id INT, v DOUBLE) DUPLICATE KEY(id) DISTRIBUTED BY HASH(id) BUCKETS 1 PROPERTIES('replication_num'='1');
INSERT INTO t VALUES (1, 5.0);  -- 单行

SELECT VAR_SAMP(v), STDDEV_SAMP(v) FROM t;
+-------------+----------------+
| VAR_SAMP(v) | STDDEV_SAMP(v) |
+-------------+----------------+
|           0 |              0 |
+-------------+----------------+
```

now:
```sql
SELECT VAR_SAMP(v), STDDEV_SAMP(v) FROM t;
+-------------+----------------+
| VAR_SAMP(v) | STDDEV_SAMP(v) |
+-------------+----------------+
|         NaN |            NaN |
+-------------+----------------+
```

doc: apache/doris-website#3765

Author: linrrzqqq

be/src/exprs/aggregate/aggregate_function_stddev.h

@@ -21,13 +21,11 @@
 #include <cmath>
 #include <cstddef>
 #include <cstdint>
+#include <limits>
 #include <memory>
-#include <type_traits>
 
 #include "core/assert_cast.h"
 #include "core/column/column.h"
-#include "core/column/column_nullable.h"
-#include "core/data_type/data_type_decimal.h"
 #include "core/data_type/data_type_number.h"
 #include "core/types.h"
 #include "exprs/aggregate/aggregate_function.h"
@@ -37,8 +35,6 @@ class Arena;
 class BufferReadable;
 class BufferWritable;
 template <PrimitiveType T>
-class ColumnDecimal;
-template <PrimitiveType T>
 class ColumnVector;
 
 template <PrimitiveType T, bool is_stddev>
@@ -71,7 +67,7 @@ struct BaseData {
             // In MySQL, this will directly result in an error due to exceeding the double range.
             // For performance reasons, we are uniformly changing it to nan
             if (std::isinf(val)) {
-                return std::nan("");
+                return std::numeric_limits<double>::quiet_NaN();
             }
             return val;
         };
@@ -125,14 +121,9 @@ struct BaseData {
 
 template <PrimitiveType T, typename Name, bool is_stddev>
 struct PopData : BaseData<T, is_stddev>, Name {
-    using ColVecResult = std::conditional_t<is_decimal(T), ColumnDecimal128V2, ColumnFloat64>;
     void insert_result_into(IColumn& to) const {
-        auto& col = assert_cast<ColVecResult&>(to);
-        if constexpr (is_decimal(T)) {
-            col.get_data().push_back(this->get_pop_result().value());
-        } else {
-            col.get_data().push_back(this->get_pop_result());
-        }
+        auto& col = assert_cast<ColumnFloat64&>(to);
+        col.get_data().push_back(this->get_pop_result());
     }
 
     static DataTypePtr get_return_type() { return std::make_shared<DataTypeFloat64>(); }
@@ -144,17 +135,12 @@ struct PopData : BaseData<T, is_stddev>, Name {
 
 template <PrimitiveType T, typename Name, bool is_stddev>
 struct SampData : BaseData<T, is_stddev>, Name {
-    using ColVecResult = std::conditional_t<is_decimal(T), ColumnDecimal128V2, ColumnFloat64>;
     void insert_result_into(IColumn& to) const {
-        auto& col = assert_cast<ColVecResult&>(to);
+        auto& col = assert_cast<ColumnFloat64&>(to);
         if (this->count == 1 || this->count == 0) {
-            col.insert_default();
+            col.get_data().push_back(std::numeric_limits<double>::quiet_NaN());
         } else {
-            if constexpr (is_decimal(T)) {
-                col.get_data().push_back(this->get_samp_result().value());
-            } else {
-                col.get_data().push_back(this->get_samp_result());
-            }
+            col.get_data().push_back(this->get_samp_result());
         }
     }