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/blocks-in-if.pug

@@ -0,0 +1,19 @@
+//- see https://github.com/pugjs/pug/issues/1589
+
+-var ajax = true
+
+-if( ajax )
+    //- return only contents if ajax requests
+    block contents
+        p ajax contents
+
+-else
+    //- return all html
+    doctype html
+    html
+        head
+            meta( charset='utf8' )
+            title sample
+            body
+                block contents
+                    p all contetns