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-parser/cases/utf8bom.tokens.json

@@ -0,0 +1,4 @@
+{"type":"tag","loc":{"start":{"line":1,"column":1},"filename":"/cases/utf8bom.pug","end":{"line":1,"column":2}},"val":"p"}
+{"type":"text","loc":{"start":{"line":1,"column":3},"filename":"/cases/utf8bom.pug","end":{"line":1,"column":8}},"val":"\"foo\""}
+{"type":"newline","loc":{"start":{"line":2,"column":1},"filename":"/cases/utf8bom.pug","end":{"line":2,"column":1}}}
+{"type":"eos","loc":{"start":{"line":2,"column":1},"filename":"/cases/utf8bom.pug","end":{"line":2,"column":1}}}