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

playground/examples/form.pug

@@ -0,0 +1,29 @@
+form(method="post")
+  fieldset
+    legend General
+    p
+      label(for="user[name]") Username:
+        input(type="text", name="user[name]", value=user.name)
+    p
+      label(for="user[email]") Email:
+        input(type="text", name="user[email]", value=user.email)
+        .tip.
+          Enter a valid 
+          email address 
+          such as <em>tj@vision-media.ca</em>.
+  fieldset
+    legend Location
+    p
+      label(for="user[city]") City:
+        input(type="text", name="user[city]", value=user.city)
+    p
+      select(name="user[province]")
+        option(value="") -- Select Province --
+        option(value="AB") Alberta
+        option(value="BC") British Columbia
+        option(value="SK") Saskatchewan
+        option(value="MB") Manitoba
+        option(value="ON") Ontario
+        option(value="QC") Quebec
+  p.buttons
+    input(type="submit", value="Save")