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

tests/check_list/nesting.html

@@ -0,0 +1,11 @@
+<ul>
+  <li>a</li>
+  <li>b</li>
+  <li>
+    <ul>
+      <li>c</li>
+      <li>d</li>
+    </ul>
+  </li>
+  <li>e</li>
+</ul>