public static BigInteger readBigIntegerLE(InputStream input, byte[] buff, int len, boolean unsigned) throws IOException {
        byte[] bytes = readNBytesLE(input, buff, 0, len);
        return unsigned ? new BigInteger(1, bytes) : new BigInteger(bytes);
    }
Reads a little-endian big integer from input stream. Uses buff to receive data from the input stream.

@param input - source of bytes
@param buff - buffer to store data
@param len - number of bytes to read
@param unsigned - whether the value is unsigned
@return - big integer value
@throws IOException
client-v2/src/main/java/com/clickhouse/client/api/data_formats/internal/BinaryStreamReader.java