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/mixins.rest-args.pug

@@ -0,0 +1,6 @@
+mixin list(tag, ...items)
+  #{tag}
+    each item in items
+      li= item
+
++list('ul', 1, 2, 3, 4)