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/sample_data/pug-lexer/cases/scripts.non-js.pug

@@ -0,0 +1,9 @@
+script#user-template(type='text/template')
+  #user
+    h1 <%= user.name %>
+    p <%= user.description %>
+
+script#user-template(type='text/template').
+  if (foo) {
+    bar();
+  }