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/fixtures/perf.pug

@@ -0,0 +1,32 @@
+.data
+  ol.sortable#contents
+    each item in report
+      if (!item.parent)
+        div
+          li.chapter(data-ref= item.id)
+            a(href='/admin/report/detail/' + item.id)
+              = item.name
+          - var chp = item.id
+            ol.sortable
+              each item in report
+                if (item.parent === chp && item.type === 'section')
+                  div
+                    li.section(data-ref= item.id)
+                      a(href='/admin/report/detail/' + item.id)
+                        = item.name
+                    - var sec = item.id
+                      ol.sortable
+                        each item in report
+                          if (item.parent === sec && item.type === 'page')
+                            div
+                              li.page(data-ref= item.id)
+                                a(href='/admin/report/detail/' + item.id)
+                                  = item.name
+                              - var page = item.id
+                                ol.sortable
+                                  each item in report
+                                    if (item.parent === page && item.type === 'subpage')
+                                      div
+                                        li.subpage(data-ref= item.id)
+                                          a(href='/admin/report/detail/' + item.id)
+                                            = item.name