fix: add scoped error logging for lexer/parser errors

- Add std.log.scoped(.pugz) to template.zig and view_engine.zig
- Log detailed error info (code, line, column, message) when parsing fails
- Log template path context in ViewEngine on parse errors
- Remove debug print from lexer, use proper scoped logging instead
- Move benchmarks, docs, examples, playground, tests out of src/ to project root
- Update build.zig and documentation paths accordingly
- Bump version to 0.3.1

examples/demo/views/layouts/base.pug

@@ -0,0 +1,28 @@
+doctype html
+html(lang="en")
+  head
+    meta(charset="UTF-8")
+    meta(name="viewport" content="width=device-width, initial-scale=1.0")
+    link(rel="stylesheet" href="/css/style.css")
+    block title
+      title Pugz Store
+  body
+    header.header
+      .container
+        .header-content
+          a.logo(href="/") Pugz Store
+          nav.nav
+            a.nav-link(href="/") Home
+            a.nav-link(href="/products") Products
+            a.nav-link(href="/about") About
+          .header-actions
+            a.cart-link(href="/cart")
+              | Cart (#{cartCount})
+
+    main
+      block content
+
+    footer.footer
+      .container
+        .footer-content
+          p Built with Pugz - A Pug template engine for Zig