fix: 内存模式下，设置单个单元格内容格式，内存模式会失效，导致内存不断堆叠溢出

[mingdiantianxia]

$config     = ['path' => '/'];
$excel = new \Vtiful\Kernel\Excel($config); 
$fileObject = $excel->constMemory('test.xlsx', '内存占用', false);
for ($index = 0; $index < 10000; $index++) {
    for ($column = 0; $column < 300; $column++) {
        $mem = self::getMemoryUsage('MemRealUsage');
        $mem = $mem / (1024 * 1024);
        $fileObject->insertText($index+1, $column, floatval($mem), 'Max$#,##0.00;Max$-#,##0.00');
        var_dump($mem);
    }
}
$filePath = $fileObject->output();
$fileObject->close();