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/examples/layout.pug

@@ -0,0 +1,14 @@
+doctype html
+html(lang="en")
+  head
+    title Example
+    script.
+      if (foo) {
+        bar();
+      }
+  body
+    h1 Pug - node template engine
+    #container
+      :markdown-it
+        Pug is a _high performance_ template engine for [node](http://nodejs.org),
+        inspired by [haml](http://haml-lang.com/), and written by [TJ Holowaychuk](http://github.com/visionmedia).