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/fixtures/issue-1593/include-layout.pug

@@ -0,0 +1,2 @@
+.included-layout
+  block include-body

tests/sample_data/pug/test/fixtures/issue-1593/include.pug

@@ -0,0 +1,4 @@
+extends ./include-layout.pug
+
+block include-body
+  .include-body

tests/sample_data/pug/test/fixtures/issue-1593/index.pug

@@ -0,0 +1,7 @@
+extends ./layout.pug
+
+block body-a
+  .body-a
+block body-b
+  .body-b
+    include ./include.pug

tests/sample_data/pug/test/fixtures/issue-1593/layout.pug

@@ -0,0 +1,3 @@
+.layout-body
+  block body-a
+  block body-b