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/attrs-data.pug

@@ -0,0 +1,7 @@
+- var user = { name: 'tobi' }
+foo(data-user=user)
+foo(data-items=[1,2,3])
+foo(data-username='tobi')
+foo(data-escaped={message: "Let's rock!"})
+foo(data-ampersand={message: "a quote: " this & that"})
+foo(data-epoc=new Date(0))