Save File Formatting %date% evaluation in Batch Queue > 1 not using time of file creation

If you use the Save File Formatting feature in the native ComfyUI Save Image node with a syntax like `%date:yyyyMMddhhmmss%` and in a Queue with a Batch Count > 1, all filenames will receive the same populated `%date%` variable.

## Example
In a queue with a batch count of > 1, all files will be named with the populated `%date%` variable of the first file indepenent of when the image file was created or the job in the queue ran.
```
myfile-20230809195712_00001_
myfile-20230809195712_00002_
myfile-20230809195712_00003_
myfile-20230809195712_00004_
...
```

I suppose `%date%` is evaluated when all jobs in a queue are created. So I'm not sure if this is a limitation of how jobs are processed in general.

Would it be possible to have the Save File Formatting variables, especially `%date%`, be populated either on the start of the current image generation in the queue or on file creation?

## Additional issues manifesting because of this
If you move or delete an image while a Queue job with a Batch count > 1 is running, the next filename that will be created fills that position.

It continuous incrementing once all missing positions in the current *numbering* have been filled. Because of this the files will no longer be sorted chronologically as they were created.

## Example

List of images in the `/output/` directory
```
myfile-20230809195712_00001_
myfile-20230809195712_00002_
myfile-20230809195712_00003_
myfile-20230809195712_00004_
...
```
If you now delete or move the file `myfile-20230809195712_00003_`, the next generated image will fill its place with the same name.
Now you have 2 images with the filename.

Solving this would make organizing and sorting of image files more robust.