Add texture loading callback for custom texture sources

[revmischa]

Adds a callback that allows applications to provide textures from non-filesystem sources like archives, network, or procedurally generated content. The callback receives the texture name and can return either raw pixel data or an existing OpenGL texture ID.

Fixes #870

[Copilot]

Pull request overview

This PR adds support for loading textures from non-filesystem sources through a callback mechanism. Applications can now provide textures from archives, network sources, or generate them procedurally. The callback can return either raw pixel data or an existing OpenGL texture ID, with automatic fallback to filesystem loading if the callback doesn't provide the requested texture.

Changes:

• Added TextureLoadCallback type and TextureLoadData structure to define the callback interface
• Extended TextureManager to try callback-based loading before filesystem loading
• Exposed the callback through both C++ (ProjectM::SetTextureLoadCallback) and C (projectm_set_texture_load_event_callback) APIs
• Updated CMakeLists.txt to install new public headers (TextureTypes.hpp, WaveformAligner.hpp, Logging.hpp)

Reviewed changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 6 comments.

Show a summary per file

File	Description
src/libprojectM/Renderer/TextureTypes.hpp	Defines TextureLoadData structure and TextureLoadCallback type for the callback interface
src/libprojectM/Renderer/TextureManager.hpp	Adds SetTextureLoadCallback method and member variable to store callback
src/libprojectM/Renderer/TextureManager.cpp	Implements callback invocation in TryLoadingTexture, checking callback before filesystem loading
src/libprojectM/ProjectM.hpp	Exposes SetTextureLoadCallback method in C++ API
src/libprojectM/ProjectM.cpp	Stores callback and ensures it's re-applied when TextureManager is recreated
src/libprojectM/ProjectMCWrapper.hpp	Adds member variables to store C callback and user data
src/libprojectM/ProjectMCWrapper.cpp	Implements C-to-C++ callback bridge with lambda wrapper
src/api/include/projectM-4/callbacks.h	Defines C API types and functions for texture loading callback
src/libprojectM/CMakeLists.txt	Adds TextureTypes.hpp, WaveformAligner.hpp, and Logging.hpp to installation list

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[kblaschke]

I do not like to talk to Coslop in code reviews...

[revmischa]

Addressed the feedback:

• Rebased on latest master
• Added m_owned member to Texture class - app-provided texture IDs now have owned=false so projectM won't delete them
• Replaced SOIL with stb_image/Texture class for creating textures from callback pixel data
• Added validation for width/height on texture ID path with warning log on failure