fix: add missing leaf span collection for final_expr_opt of asm blocks (

FuelLabs#3041)

closes FuelLabs#2716.

examples/asm_return_tuple_pointer/src/main.sw

@@ -12,7 +12,7 @@ fn adder(a: u64, b: u64, c: u64) -> (u64, u64) {
 }
 
 fn main() -> bool {
-    let(first, second) = adder(1, 2, 3);
+    let (first, second) = adder(1, 2, 3);
     assert(first == 3);
     assert(second == 5);
     true

swayfmt/src/utils/language/expr/asm_block.rs

@@ -214,6 +214,9 @@ impl LeafSpans for AsmBlockContents {
         for instruction in &self.instructions {
             collected_spans.append(&mut instruction.leaf_spans());
         }
+        if let Some(final_expr) = &self.final_expr_opt {
+            collected_spans.append(&mut final_expr.leaf_spans());
+        }
         collected_spans
     }
 }