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/case.pug

@@ -0,0 +1,19 @@
+html
+  body
+    - var friends = 1
+    case friends
+      when 0: p you have no friends
+      when 1: p you have a friend
+      default: p you have #{friends} friends
+    - var friends = 0
+    case friends
+      when 0
+      when 1
+        p you have very few friends
+      default
+        p you have #{friends} friends
+
+    - var friend = 'Tim:G'
+    case friend
+      when 'Tim:G':    p Friend is a string
+      when {tim: 'g'}: p Friend is an object