mrc-5483: Fix issue when pulling multiple packets with multiple files

[r-ash]

Issue spotted by Jeff when pulling packets

> orderly2::orderly_location_pull_packet(name = "split_model_results")
Error in data.frame(..., stringsAsFactors = FALSE, check.names = FALSE) : 
  arguments imply differing number of rows: 537, 31

> traceback()
6: stop(gettextf("arguments imply differing number of rows: %s", 
       paste(unique(nrows), collapse = ", ")), domain = NA)
5: data.frame(..., stringsAsFactors = FALSE, check.names = FALSE)
4: data_frame(hash = unlist(lapply(meta, function(x) x$files$hash), 
       FALSE, FALSE), size = unlist(lapply(meta, function(x) x$files$size), 
       FALSE, FALSE), location = location_use)
3: location_build_pull_plan_files(packets$fetch, location, root, 
       call)
2: location_build_pull_plan(ids, options$locations, recursive, root, 
       call = environment())
1: orderly2::orderly_location_pull_packet(name = "split_model_results")

This is happening because if we pull with a query which finds multiple packets which are at more than 1 location then we're not matching up the location to the file information correctly. In particular, if the packets have a total number of files which is not a multiple of the number of locations then this errors 🙈 Expect we've not seen this in our other tests because we're always creating 1 file in the test data. This PR adds a test to recreate the issue and fixes it.

I tidied up the docs here a little bit too. But Jeff was definitely a bit confused about this interface, he was expecting passing name = "..." to only pull the latest with that name. It wasn't immediately obvious to him that this would pull all of them, and I can see why. Will leave this for @M-Kusumgar to discuss

[richfitz]

Mantra and I discussed adding a latest = helper here too, in the same way as name is a helper

[richfitz]

This issue also turns up in #144 and #146 implicitly in that we might want a "pull exactly one" vs "pull all that match" interface

[richfitz]

clearly our idea and implementation have drifted apart at some point