Users want to get rounding mode in `quantileExact` equivalent to "median_low" from Python:
https://docs.python.org/3/library/statistics.html#statistics.median_low
while current implementation works equivalent to "median_high" (?)
#pragma once
#include <Common/PODArray.h>
#include <Common/NaNUtils.h>
#include <Core/Types.h>
#include <IO/WriteBuffer.h>
#include <IO/ReadBuffer.h>
#include <IO/VarInt.h>
namespace DB
{
namespace ErrorCodes
{
    extern const int NOT_IMPLEMENTED;
    extern const int BAD_ARGUMENTS;
}
/** Calculates quantile by collecting all values into array
  *  and applying n-th element (introselect) algorithm for the resulting array.
  *
  * It uses O(N) memory and it is very inefficient in case of high amount of identical values.
  * But it is very CPU efficient for not large datasets.
  */
template <typename Value>
struct QuantileExact
{
    
    static constexpr size_t bytes_in_arena = 64 - sizeof(PODArray<Value>);
    using Array = PODArrayWithStackMemory<Value, bytes_in_arena>;
    Array array;
    void add(const Value & x)