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.pug

@@ -0,0 +1,10 @@
+p= null
+p= undefined
+p= ''
+p= 0
+p= false
+p(foo=null)
+p(foo=undefined)
+p(foo='')
+p(foo=0)
+p(foo=false)