feat(image): enhance image handling with new properties and responsive support

- Updated PostEntry type to include _rawImageUrl and _imageFocal for improved image management.
- Refactored image handling in various components to utilize the new properties, ensuring better focal point support and responsive image rendering.
- Introduced warmResponsiveImage function for pre-fetching image variants to optimize loading performance.
- Replaced CmsImage component with RustyImage in multiple blocks for consistent image processing.

src/lib/image-cache.server.ts

@@ -36,8 +36,7 @@ const memoryCache = new Map<string, CachedImage>();
 let resolvedDir: string | null = null;
 
 function ensureCacheDir(): string {
-  if (resolvedDir) return resolvedDir;
-  const dir = join(process.cwd(), CACHE_DIR);
+  const dir = resolvedDir ?? join(process.cwd(), CACHE_DIR);
   if (!existsSync(dir)) mkdirSync(dir, { recursive: true });
   resolvedDir = dir;
   return dir;