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/test/anti-cases/readme.md

@@ -0,0 +1 @@
+This folder collects examples of files that are not valid `pug`, but were at some point accepted by the parser without throwing an error.  The tests ensure that all these cases now throw some form of error message (hopefully a helpful one).