fix: merge multiple class attributes in zig_codegen (compiled templates)

- zig_codegen.zig: collect and merge class values in both static and dynamic attribute paths
- Completes the fix for multiple classes (.a.b -> class="a b") across all rendering modes

build.zig.zon

@@ -1,6 +1,6 @@
 .{
     .name = .pugz,
-    .version = "0.3.4",
+    .version = "0.3.5",
     .fingerprint = 0x822db0790e17621d, // Changing this has security and trust implications.
     .minimum_zig_version = "0.15.2",
     .dependencies = .{},