ncbi_recover_id() should not recover pubmed urls

While this works:

``` r
ncbi_recover_id("39332413", db = "pubmed")
[1] "https://doi.org/10.1016/j.cell.2024.09.009"
```

On second thought, this function should return NCBI IDs. An article DOI is not an NCBI ID. This is confusing. Maybe we should have an ncbi_get_doi() function or something else instead.