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

benchmarks/templates/simple-2.pug

@@ -0,0 +1,10 @@
+div
+  h1.header #{header}
+  h2.header2 #{header2}
+  h3.header3 #{header3}
+  h4.header4 #{header4}
+  h5.header5 #{header5}
+  h6.header6 #{header6}
+  ul.list
+    each item in list
+      li.item #{item}