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/test/browser/index.pug

@@ -0,0 +1,20 @@
+!!! 5
+html
+  head
+  body
+    textarea#input(placeholder='write pug here', style='width: 100%; min-height: 400px;').
+      p
+        author
+          != myName
+    pre(style='background: #ECECEC;width: 100%; min-height: 400px;')
+      code#output
+    script(src='../../pug.js')
+    script.
+      var input = document.getElementById('input');
+      var output = document.getElementById('output');
+      setInterval(function () {
+        pug.render(input.value, {myName: 'Forbes Lindesay', pretty: true}, function (err, res) {
+          if (err) throw err;
+          output.textContent = res;
+        })
+      }, 500)