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

benchmarks/templates/projects-escaped.pug

@@ -0,0 +1,11 @@
+doctype html
+html
+  head
+    title #{title}
+  body
+    p #{text}
+    each project in projects
+      a(href=project.url) #{project.name}
+      p #{project.description}
+    else
+      p No projects