fix(acir_gen): Nested dynamic array initialization (#5810)

# Description

## Problem\*

Resolves #5782 

## Summary\*

We are using our recursive `initialize_array_inner` function to also
check whether the outer AcirValue we are trying to initialize is a
dynamic array. We should be able to initialize a new AcirValue::Array
with internal AcirValue::DynamicArray types.

## Additional Context



## Documentation\*

Check one:
- [X] No documentation needed.
- [ ] Documentation included in this PR.
- [ ] **[For Experimental Features]** Documentation to be submitted in a
separate PR.

# PR Checklist\*

- [X] I have tested the changes locally.
- [X] I have formatted the changes with [Prettier](https://prettier.io/)
and/or `cargo fmt` on default settings.

compiler/noirc_evaluator/src/ssa/acir_gen/acir_ir/acir_variable.rs

@@ -1933,6 +1933,9 @@ impl<F: AcirField> AcirContext<F> {
             }
             Some(optional_value) => {
                 let mut values = Vec::new();
+                if let AcirValue::DynamicArray(_) = optional_value {
+                    unreachable!("Dynamic array should already be initialized");
+                }
                 self.initialize_array_inner(&mut values, optional_value)?;
                 values
             }
@@ -1962,8 +1965,16 @@ impl<F: AcirField> AcirContext<F> {
                     self.initialize_array_inner(witnesses, value)?;
                 }
             }
-            AcirValue::DynamicArray(_) => {
-                unreachable!("Dynamic array should already be initialized");
+            AcirValue::DynamicArray(AcirDynamicArray { block_id, len, .. }) => {
+                let dynamic_array_values = try_vecmap(0..len, |i| {
+                    let index_var = self.add_constant(i);
+
+                    let read = self.read_from_memory(block_id, &index_var)?;
+                    Ok::<AcirValue, InternalError>(AcirValue::Var(read, AcirType::field()))
+                })?;
+                for value in dynamic_array_values {
+                    self.initialize_array_inner(witnesses, value)?;
+                }
             }
         }
         Ok(())

test_programs/execution_success/nested_dyn_array_regression_5782/Nargo.toml

@@ -0,0 +1,7 @@
+[package]
+name = "nested_dyn_array_regression_5782"
+type = "bin"
+authors = [""]
+compiler_version = ">=0.33.0"
+
+[dependencies]

test_programs/execution_success/nested_dyn_array_regression_5782/Prover.toml

@@ -0,0 +1,2 @@
+array = [5, 10]
+i = 1

test_programs/execution_success/nested_dyn_array_regression_5782/src/main.nr

@@ -0,0 +1,13 @@
+fn main(mut array: [Field; 2], i: u32) {
+    assert_eq(array[i - 1], 5);
+    assert_eq(array[i], 10);
+
+    array[i] = 2;
+
+    let array2 = [array, array];
+
+    assert_eq(array2[0][0], 5);
+    assert_eq(array2[0][i], 2);
+    assert_eq(array2[i][0], 5);
+    assert_eq(array2[i][i], 2);
+}