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

examples/demo/views/includes/other.pug

@@ -0,0 +1,2 @@
+.p
+  | some other thing

examples/demo/views/includes/some_partial.pug

@@ -0,0 +1,4 @@
+.info-box
+  h3 Included Partial
+  p This content comes from includes/some_partial.pug
+  p It demonstrates the include directive for reusable template fragments.