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/comments-in-case.pug

@@ -0,0 +1,10 @@
+doctype html
+html
+  body
+   - var s = 'this'
+   case s
+     //- Comment
+     when 'this'
+       p It's this!
+     when 'that'
+       p It's that!