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-lexer/cases/attrs.js.pug

@@ -0,0 +1,22 @@
+- var id = 5
+- function answer() { return 42; }
+a(href='/user/' + id, class='button')
+a(href  =  '/user/' + id, class  =  'button')
+meta(key='answer', value=answer())
+a(class = ['class1', 'class2'])
+a.tag-class(class = ['class1', 'class2'])
+
+a(href='/user/' + id class='button')
+a(href  =  '/user/' + id class  =  'button')
+meta(key='answer' value=answer())
+a(class = ['class1', 'class2'])
+a.tag-class(class = ['class1', 'class2'])
+
+div(id=id)&attributes({foo: 'bar'})
+- var bar = null
+div(foo=null bar=bar)&attributes({baz: 'baz'})
+
+div(...object)
+div(...object after="after")
+div(before="before" ...object)
+div(before="before" ...object after="after")