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/block-code.pug

@@ -0,0 +1,12 @@
+-
+  list = ["uno", "dos", "tres",
+          "cuatro", "cinco", "seis"];
+//- Without a block, the element is accepted and no code is generated
+-
+each item in list
+  -
+    string = item.charAt(0)
+    
+      .toUpperCase() +
+    item.slice(1);
+  li= string