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/pages/include-demo.pug

@@ -0,0 +1,20 @@
+extends layouts/base.pug
+
+block title
+  title Include Demo | Pugz Store
+
+block content
+  section.page-header
+    .container
+      h1 Include Demo
+      p Demonstrating the include directive
+
+  section.section
+    .container
+      h2 Content from this page
+      p The box below is included from a separate partial file.
+
+      include includes/some_partial.pug
+
+      h2 After the include
+      p This content comes after the included partial.