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/check_list/html.pug

@@ -0,0 +1,13 @@
+- var version = 1449104952939
+
+<ul>
+  <li>foo</li>
+  <li>bar</li>
+  <li>baz</li>
+</ul>
+
+<!--build:js /js/app.min.js?v=#{version}-->
+<!--endbuild-->
+
+p You can <em>embed</em> html as well.
+p: <strong>Even</strong> as the body of a block expansion.