feat: add template inheritance (extends/block) support

- ViewEngine now supports extends and named blocks
- Each route gets exclusive cached AST (no shared parent layouts)
- Fix iteration over struct arrays in each loops
- Add demo app with full e-commerce layout using extends
- Serve static files from public folder
- Bump version to 0.3.0

src/tests/test_includes.zig

@@ -0,0 +1,24 @@
+const std = @import("std");
+const pugz = @import("pugz");
+
+pub fn main() !void {
+    var gpa = std.heap.GeneralPurposeAllocator(.{}){};
+    defer _ = gpa.deinit();
+    const allocator = gpa.allocator();
+
+    var engine = pugz.ViewEngine.init(allocator, .{
+        .views_dir = "test_views",
+    }) catch |err| {
+        std.debug.print("Init Error: {}\n", .{err});
+        return err;
+    };
+    defer engine.deinit();
+
+    const html = engine.render(allocator, "home", .{}) catch |err| {
+        std.debug.print("Error: {}\n", .{err});
+        return err;
+    };
+    defer allocator.free(html);
+
+    std.debug.print("=== Rendered HTML ===\n{s}\n=== End ===\n", .{html});
+}