fixed usage of for iterator variable

corelib/src/test/array_test.cairo

@@ -216,3 +216,14 @@ fn test_array_snap_into_span() {
 fn test_span_into_array_snap() {
     assert_eq!(@array![1, 2, 3], array![1, 2, 3].span().into());
 }
+#[test]
+fn nested_for_loop() {
+    let mat = array![array![1, 2], array![3, 4], array![5, 6]];
+    let mut result = 0;
+    for arr in mat {
+        for i in arr {
+            result += i;
+        };
+    };
+    assert_eq!(result, 21);
+}

crates/cairo-lang-lowering/src/lower/test_data/usage

@@ -124,3 +124,48 @@ Block 6:27:
   Usage: ParamId(test::a)::b::c, 
   Changes: ParamId(test::a)::b::c, 
   Introductions: LocalVarId(test::c), LocalVarId(test::only_used_in_condition),
+
+//! > ==========================================================================
+
+//! > Test for usage
+
+//! > test_runner_name
+test_function_usage
+
+//! > function
+fn foo(a: u32) {
+    let arr = array![1, 2, 3];
+    for b in arr {
+        a + b;
+    };
+}
+
+//! > function_name
+foo
+
+//! > module_code
+
+//! > semantic_diagnostics
+
+//! > usage
+Block 0:0:
+  Usage:
+  Changes:
+  Snapshot_Usage:
+  Introductions: LocalVarId(test::__array_builder_macro_result__),
+Block 2:17:
+  Usage: ParamId(test::a), LocalVarId(test::b),
+  Changes:
+  Snapshot_Usage:
+  Introductions:
+For 2:4:
+  Usage: LocalVarId(test::in), ParamId(test::a),
+  Changes: LocalVarId(test::in),
+  Snapshot_Usage:
+  Introductions: LocalVarId(test::b),
+Block 0:15:
+  Usage: ParamId(test::a),
+  Changes:
+  Snapshot_Usage:
+  Introductions: LocalVarId(test::arr), LocalVarId(test::in),
+

crates/cairo-lang-lowering/src/lower/usage.rs

@@ -8,6 +8,7 @@ use cairo_lang_semantic::{
     self as semantic, Expr, ExprFunctionCallArg, ExprId, ExprVarMemberPath, FunctionBody, Pattern,
     Statement, VarId,
 };
+use cairo_lang_utils::extract_matches;
 use cairo_lang_utils::ordered_hash_map::OrderedHashMap;
 use cairo_lang_utils::ordered_hash_set::OrderedHashSet;
 use id_arena::Arena;
@@ -209,6 +210,9 @@ impl BlockUsages {
                 self.block_usages.insert(expr_id, usage);
             }
             Expr::For(expr) => {
+                current.introductions.insert(
+                    extract_matches!(&expr.into_iter_member_path, ExprVarMemberPath::Var).var,
+                );
                 let mut usage: Usage = Default::default();
                 usage.usage.insert(
                     (&expr.into_iter_member_path).into(),