Fix the `--no-default-features` test(s)

Currently, building with `--no-default-features` is throwing an error due to undeclared allocators.

```bash

```

## Reproducing

1. Run `cargo test --no-default-features --workspace`
4. See error

### Expected

The crate should compile, using the `nightly` feature flag to enable additional "experimental" features like `#[feature(allocator_api)]`
