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/code.pug

@@ -0,0 +1,17 @@
+
+- var title = "Things"
+
+-
+  var subtitle = ["Really",  "long",
+                  "list", "of",
+                  "words"]
+h1= title
+h2= subtitle.join(" ")
+
+ul#users
+  each user, name in users
+    // expands to if (user.isA == 'ferret')
+    if user.isA == 'ferret'
+      li(class='user-' + name) #{name} is just a ferret
+    else
+      li(class='user-' + name) #{name} #{user.email}