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-es2015/attr.html

@@ -0,0 +1 @@
+<div class="avatar-div" style="background-image: url(https://www.gravatar.com/avatar/219b77f9d21de75e81851b6b886057c7)"></div>

tests/sample_data/pug/test/cases-es2015/attr.pug

@@ -0,0 +1,3 @@
+- var avatar = '219b77f9d21de75e81851b6b886057c7'
+
+div.avatar-div(style=`background-image: url(https://www.gravatar.com/avatar/${avatar})`)