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/mixin.attrs.pug

@@ -0,0 +1,59 @@
+mixin centered(title)
+  div.centered(id=attributes.id)
+    - if (title)
+      h1(class=attributes.class)= title
+    block
+    - if (attributes.href)
+      .footer
+        a(href=attributes.href) Back
+
+mixin main(title)
+  div.stretch
+    +centered(title).highlight&attributes(attributes)
+      block
+
+mixin bottom
+  div.bottom&attributes(attributes)
+    block
+
+body
+  +centered#First Hello World
+  +centered('Section 1')#Second
+    p Some important content.
+  +centered('Section 2')#Third.foo(href='menu.html', class='bar')
+    p Even more important content.
+  +main('Section 3')(href='#')
+    p Last content.
+  +bottom.foo(class='bar', name='end', id='Last', data-attr='baz')
+    p Some final words.
+  +bottom(class=['class1', 'class2'])
+
+mixin foo
+  div.thing(attr1='foo', attr2='bar')&attributes(attributes)
+
+- var val = '<biz>'
+- var classes = ['foo', 'bar']
++foo(attr3='baz' data-foo=val data-bar!=val class=classes).thunk
+
+//- Regression test for #1424
+mixin work_filmstrip_item(work)
+  div&attributes(attributes)= work
++work_filmstrip_item('work')("data-profile"='profile', "data-creator-name"='name')
+
+mixin my-mixin(arg1, arg2, arg3, arg4)
+  p= arg1
+  p= arg2
+  p= arg3
+  p= arg4
+
++foo(
+  attr3="qux"
+  class="baz"
+)
+
++my-mixin(
+'1',
+      '2',
+  '3',
+      '4'
+)