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/cases/mixins.pug

@@ -0,0 +1,32 @@
+mixin comment(title, str)
+  .comment
+    h2= title
+    p.body= str
+
+
+mixin comment (title, str)
+  .comment
+    h2= title
+    p.body= str
+
+#user
+  h1 Tobi
+  .comments
+    +comment('This',
+            (('is regular, javascript')))
+
+mixin list
+  ul
+    li foo
+    li bar
+    li baz
+
+body
+  +list()
+  + list()
+
+mixin foobar(str)
+  div#interpolation= str + 'interpolated'
+
+- var suffix = "bar"
++#{'foo' + suffix}('This is ')