Waddy: Add Recursive Import

[G2Pavon]

Added find_files_recursively() in src\utils\misc.rs. So it can be used in other gchimp modules too

also used walkdir, since apparently it's fast enough, and it also handles complex cases like many subdirs and symslinks

This feature it's a bit slow, but that's probably a limitation of egui i think. It's probably possible to speed up this, but idk how :/

[khanghugo]

The bottleneck here is not the walkdir or IO but it is the computation. Usually, what I'd do is to use rayon to speedup processing images.

If you are invested in this, you should process all images in parallel using rayon and then modify WaddyGui::update_after_add_image to load all images together.

This is probably require a bit more work but the current implementation is fine.

[khanghugo]

Currently, there are lots of work to load an image into Waddy.

1. Feed a path
2. Decode / deserialize image (heavy)
3. Convert to 8 bit per pixel (heavy)
4. Store it in WAD
5. Convert new WAD entry into RGB8 again
6. Create a new texture from RGB8 (just a lookup table, not heavy)
7. Display RGB8 texture on Waddy

So, there are 3 2 heavy computations happening.

Due to the way how Waddy is designed, can't do it in 2 heavy computations.

And if anything, Waddy could be changed a bit to accommodate loading more than 1 texture at a time to support rayon