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/check_list/code.conditionals.pug

@@ -0,0 +1,43 @@
+
+- if (true)
+  p foo
+- else
+  p bar
+
+- if (true) {
+  p foo
+- } else {
+  p bar
+- }
+
+if true
+  p foo
+  p bar
+  p baz
+else
+  p bar
+
+unless true
+  p foo
+else
+  p bar
+
+if 'nested'
+  if 'works'
+    p yay
+
+//- allow empty blocks
+if false
+else
+  .bar
+if true
+  .bar
+else
+.bing
+
+if false
+  .bing
+else if false
+  .bar
+else
+  .foo