added base64 image extraction feature in markdown conversion

[untko]

Title: added base64 image extraction in the ipynb files

Problem

When converting notebooks to markdown, the current implementation has issues with:

• base64 embedded images are not exported and left as it is. Only images linked with files or within ipynb are extracted.
• it leads to markdown files with base64 images not being rendered in some reader.
• Only IDEs can render it afaik.
• 0ther markdown readers (iA readers, marktext ...) can't render the base64 image inside the md files. which leads to

Solution

• Added extraction of base64 embedded images as their original format (jpg, png, ...)

• and replaced the base64 image as directory in the new markdown file,

example
-, instead of
![image.png](data:image/png;base64,iVBORw0KGgoAAAA...]

• Duplicate filename conflicts occured when also extracting base64 images -> Added timestamp to ensure unique filenames and improved output directory path handling

Testing

• Tested with notebooks containing multiple images, with
• test file "notebook_with_base64.ipynb" inside test/file and
• test_extractbase64images.py for checking it.
• Verified correct image path resolution

Related Issues

Fixes issue with duplicate filenames and image path resolution in markdown export (likely caused by additional extraction of base64 images)

side note

• This is my very first time for a pull request, so please bear with me and guide me if i'm not following standard practice.