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/if-expression.pug

@@ -0,0 +1,13 @@
+each account in accounts
+  div
+    if account.status == "closed"
+      div Your account has been closed!
+    if account.status == "suspended"
+      div Your account has been temporarily suspended
+    if account.status == "open"
+      div
+        | Bank balance:
+        if account.negative
+          span.negative= account.balanceFormatted
+        else
+          span.positive= account.balanceFormatted