Question/Feature Request: download SharePoint List attachment

Scenario: user adds a record in SharePoint List and upload files as attachment.

Goal: be able to download attachments into an R session.

#### Current State
Able to show that attachments exist, but no method to list attachments' URL or download them.

SharePoint attachments don't seem to be stored in any of the _drives_ either, so can't get from there.

```r
my_site <- Microsoft365R::sharepoint_site(
site_url = config::get("sp_site"),
app = AzureGraph:::.az_cli_app_id
)

data_raw <- my_site$get_list("List")$list_items()

data_raw %>%
select(id, Attachments)

# _List_ showing attachments
#> id Attachments
#> 1 7 FALSE
#> 2 8 TRUE

# _List_ folder showing empty even though it has attachments
my_site$get_drive()$list_files()
name size isdir
1 General 16643828 TRUE
2 List 0 TRUE
3 Weekly Report 12600039 TRUE
4 Untitled.png 8835 FALSE
```

Start with the Microsoft365R::sharepoint_site entry point and the get_list("List")$list_items() and get_drive() calls shown in the report. Investigate how SharePoint list-item attachments are exposed, then provide a way to enumerate their URLs and download them into an R session. Done means attachments are discoverable and downloadable even though the list's drive is empty.

Written by the indexing model from the issue text.