feat: add free_sd_images function to manage memory for C API

[Cyberhan123]

Summary

This is part of #1368.
This pull request introduces a new memory management function to the C API for handling image arrays, which is especially important for Windows compatibility. The main change is the addition of a free_sd_images function to safely free memory allocated for image arrays, preventing issues related to mismatched C runtime libraries.

Memory management improvements

• Added a new API function free_sd_images to both the stable-diffusion.h header and the implementation in stable-diffusion.cpp. This function ensures that memory allocated for image arrays (sd_image_t*) is properly freed, addressing potential CRT (C Runtime) issues on Windows when memory is allocated in the library but freed in the caller.

Checklist

• I have read and confirmed this PR follows the contribution guidelines.

[Copilot]

Pull request overview

Note

Copilot was unable to run its full agentic suite in this review.

Adds a C-API helper to centralize deallocation of image buffers returned by the library, primarily to avoid Windows CRT mismatches when callers free memory allocated inside the DLL.

Changes:

• Added free_sd_images(sd_image_t* result_images, int num_images) implementation to free per-image buffers plus the image array.
• Exposed the new function in the public header with guidance for C API callers.

Reviewed changes

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

File	Description
src/stable-diffusion.cpp	Implements free_sd_images to free image data buffers and the containing array.
include/stable-diffusion.h	Declares the new API and documents intended ownership/freeing pattern for C callers.

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