Rework image_view with AdwCarousel, LpImagePage, and LpFileModel

Previously we loaded images synchronously and manually changed LpImage. This could cause freezes when loading large images and SVGs. We also had no proper feedback for when a corrupted or unsupported image was loaded.

This commit introduces a major rework to how we handle images and the gallery. It introduces a swipeable gallery that loads files asynchronously via a new widget: LpImagePage.

LpImagePage owns the file and information related to the file, and on creation it spawns a future that either loads an error page when it can't load something (file deleted, corrupted, or unsupported) or the actual image via LpImage. LpImagePage now holds the right-click popover and the associated gestures.

The gestures needed to be moved to LpImagePage in order to rework LpImageView's overlay - instead of having an overlay child that's a box with a few buttons, we now have the buttons as individual overlay children. This could cause them to overlap each other at certain sizes, but it's required in order to allow input to reach the carousel below.

Right now this comes with a few regressions:

• Occasionally input gets blocked across the application window. It's hard to tell if this is caused by swipes or right clicking. This input issue can cause a crash - no Rust backtrace, so a debugger is needed.

• The "current" page doesn't seem to be properly loaded by the time set_image_from_file () finishes, so we need to rework resizing from image dimensions

• We need to re-implement loading different directories and files within directories

There also seems to be an issue on touchscreens, swiping between images on a touchscreen causes responsiveness issues not present when swiping on a touchpad. My guess is that it's related to the long press gesture.