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

playground/examples/rss.pug

@@ -0,0 +1,14 @@
+doctype xml
+rss(version='2.0')
+channel
+  title RSS Title
+  description Some description here
+  link http://google.com
+  lastBuildDate Mon, 06 Sep 2010 00:01:00 +0000
+  pubDate Mon, 06 Sep 2009 16:45:00 +0000
+
+  each item in items
+    item
+      title= item.title
+      description= item.description
+      link= item.link