Fix array initializer type casting and multidimensional array initialization

[Copilot]

int arr[2] = {2.0f, 3.0f} silently produces zeroes because DoEmitStructureAssignment emits initializer values without casting to the target element type. Multidimensional array init (int a[2][3] = {{1,2,3},{4,5,6}}) also fails because the read path unconditionally dereferences element pointers even when the element is itself an array.

Changes

• AssignExpression.cs — Add EmitCast from each item's type to the array element type. Extract recursive EmitArrayStructuredInit to walk nested StructureExpression nodes for multidimensional arrays.
• ArrayElementExpression.cs — Skip LoadPointer when the evaluated element type is CArrayType (array-to-pointer decay instead of value load).
• ArrayTests.cs — Tests for float→int, double→int, int→float array init, and 2D array init (global + local).

// Previously: arr[0] == 0, arr[1] == 0 (float bits stored as int)
// Now: arr[0] == 2, arr[1] == 3 (proper truncation)
int arr[2] = {2.0f, 3.0f};

// Previously: not supported
// Now: works correctly
int a[2][3] = {{1, 2, 3}, {4, 5, 6}};