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/includes.pug

@@ -0,0 +1,10 @@
+
+include auxiliary/mixins.pug
+
++foo
+
+body
+  include auxiliary/smile.html
+  include auxiliary/escapes.html
+  script(type="text/javascript")
+    include:verbatim auxiliary/includable.js