fix: add dispose() methods to prevent VRAM/GTT memory leaks

[bechampion]

Summary

This PR adds proper dispose() methods to several widget classes to prevent GPU memory (VRAM/GTT) leaks when notifications and media players are created and destroyed.

Problem

Over time, swaync accumulates GPU memory (observable via /sys/class/drm/card*/device/mem_info_vram_used or GTT usage) due to:

1. Notification images not being cleared - When notifications with images are dismissed or replaced, the Gdk.Texture objects backing img, img_app_icon, and body_image are not explicitly released
2. MPRIS album art textures accumulating - When media players update album art, new textures are created without clearing the previous ones
3. Widget children not properly unparented - The Underlay class (parent of MprisPlayer) doesn't clean up its children on disposal
4. Animation references preventing GC - NotificationGroup animations can hold references that prevent garbage collection

Changes

src/notification/notification.vala

• Added dispose() method that clears img, img_app_icon, body_image, removes pending timeouts, and nulls gesture/controller references
• Added body_image.set_paintable(null) before setting new paintable in set_body()

src/controlCenter/widgets/mpris/mpris_player.vala

• Added dispose() method that calls before_destroy()
• Enhanced before_destroy() to cancel ongoing downloads and clear album_art/background_picture textures
• Added texture clearing before loading new album art in update_album_art()

src/underlay/underlay.vala

• Added dispose() method that properly unparents both _child and _underlay_child

src/notificationGroup/notificationGroup.vala

• Added dispose() method that skips/nulls animations, disconnects handlers, and clears collections

Testing

Tested by monitoring VRAM usage while:

• Sending many notifications with images and dismissing them
• Playing media with frequently changing album art
• Expanding/collapsing notification groups

GPU memory now stabilizes after dismissal instead of continuously growing.

Technical Details

In GTK4/Wayland, Gdk.Texture objects are backed by GPU memory. When new paintables are assigned to Gtk.Image or Gtk.Picture widgets without clearing the old ones first, or when widgets are destroyed without explicit cleanup, the GPU memory may not be immediately released due to:

• GObject reference counting keeping textures alive
• GTK4's paintable system holding references
• Vala's garbage collection timing
• Animation targets holding widget references

The dispose() pattern ensures deterministic cleanup of GPU resources when widgets are destroyed.

[Copilot]

Pull request overview

This PR adds dispose() methods to four widget classes to prevent GPU memory (VRAM/GTT) leaks when notifications and media players are created and destroyed repeatedly. The changes ensure that Gdk.Texture objects and related GPU resources are explicitly released rather than relying on garbage collection timing.

Changes:

• Added dispose() methods to properly release GPU textures and other resources in notification, media player, and widget classes
• Added preemptive texture clearing before loading new images in notification bodies and MPRIS album art
• Enhanced MPRIS player cleanup to cancel ongoing downloads and clear textures on destruction

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.

File	Description
src/underlay/underlay.vala	Added dispose() method to properly unparent both child and underlay_child widgets
src/notificationGroup/notificationGroup.vala	Added dispose() method to stop animations and clear collections; includes extensive whitespace formatting changes
src/notification/notification.vala	Added dispose() method to clear image resources and remove timeouts; added body_image clearing before loading new textures
src/controlCenter/widgets/mpris/mpris_player.vala	Added dispose() method calling before_destroy(); enhanced before_destroy() to cancel downloads and clear album art textures; added texture clearing before loading new album art

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