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/interpolated-mixin.pug

@@ -0,0 +1,4 @@
+mixin linkit(url)
+  a(href=url)= url
+
+p This also works #[+linkit('http://www.bing.com')] so hurrah for Pug