### opt · function

Create an optional type wrapper (allows undefined).

**Signature:** `<const T extends TypeWrapper<unknown> | BasicType>(inner: T) => TypeWrapper<T extends TypeWrapper<infer U> ? U : T>`

**Type Parameters:**

- `T extends TypeWrapper<unknown>|BasicType` - Type wrapper or basic type to make optional.

**Parameters:**

- `inner: T` - The inner type to make optional.

**Returns:** A union type that accepts the inner type or undefined.

**Examples:**

```typescript
const optionalString = E.opt(E.string);
const optionalNumber = E.opt(E.number);
```