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-debug.js

@@ -0,0 +1,10 @@
+/**
+ * Module dependencies.
+ */
+
+var pug = require('../');
+
+pug.renderFile(__dirname + '/layout.pug', {debug: true}, function(err, html) {
+  if (err) throw err;
+  console.log(html);
+});