Crash if there is an error in batch addition.
Example:

```
const usearch = require('usearch');
const index = new usearch.Index({ metric: 'l2sq', connectivity: 16, dimensions: 3 });
index.add(42n, new Float32Array([0.2, 0.6, 0.4]));
index.add(
  [41n, 42n, 43n],
  [[0.1, 0.6, 0.4], [0.2, 0.6, 0.4], [0.3, 0.6, 0.4]]
)
```

`42n` is duplicated, which causes an error, but then it crash.

It seems that it is not better to throw an exception during the process,
so we changed it to throw it after it is completed.