Partial fixes and clarifications for issues raised in #30

[Zador-Pataki]

This PR addresses parts of #30. Specifically:

• Fixes broken instructions in the README and example scripts (pending feedback)
• Notes the need for p7zip-full when extracting ETH3D .7z archives (pending feedback)
• Fixes a minor bug in SimpleTest

Some changes are provisional — feedback welcome before finalizing.

[PoyrazTahan]

@Zador-Pataki Great work on the initial fixes for issue #30! I've tested your
changes and extended them with some additional improvements that follow your exact
approach.

What I Added (Building on Your Work):

Completed your Path conversion pattern:

# Your original lines 26-27 in simple.py:
cache_dir = Path(cache_dir) if cache_dir is not None else None
images_dir = Path(images_dir) if images_dir is not None else None

# I extended with the same pattern for remaining parameters:
intrinsics_pth = Path(intrinsics_pth) if intrinsics_pth is not None else None
refrec_dir = Path(refrec_dir) if refrec_dir is not None else None

Additional bug fixes:

• Fixed variable typo imanme → imname in SimpleParser
• Improved intrinsics loading logic to handle both provided and default paths
• Added multi-reconstruction script for easier testing

My Fork with Changes:

• Repository: https://github.com/PoyrazTahan/mpsfm/tree/pr-31-fixes
• Commit: f26038b

The changes strictly follow your coding style and complete the Path conversion
approach you started. This should resolve more of the issues mentioned in #30.

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I also completed the code for ply, gltf, colmap output (dense points with camera location and textures). They are easier to peek and inspect compared to html. I would like to merge them as well to be able to showcase your work better. Let' me know how you would like to coordinate the project