Question/Feature request: Sync/merge contacts from a Google/iCloud .vcf export/backup

I'm looking to find out if import/sync can be done between a unified .vcf file obtained as export/backup from Google/iCloud/etc.

I presume the singlefile storage type was created for this, but using a config file: ~/.config/vdirsyncer/config:

[general]
status_path = "~/.vdirsyncer/status/"

[pair alex_contacts]
a = "contacts_local"
b = "google_backup"
collections = ["from a", "from b"]
metadata = ["color"]

[storage contacts_local]
type = "filesystem"
path = "~/.contacts/"
fileext = ".vcf"

[storage google_backup]
type = "singlefile"
path = "<path to google export of contacts file>.vcf"

Having output:

$ vdirsyncer -v DEBUG discover
Discovering collections for pair alex_contacts
contacts_local:
google_backup:
Saved for alex_contacts: collections = []

vdirsyncer version: 0.19.1
Server: iCloud/Google export/backup as .vcf
Python version: 3.10.10
OS: arch

Start with the singlefile storage documentation linked in the issue and reproduce the supplied configuration with vdirsyncer -v DEBUG discover. Trace how the filesystem and singlefile storages enumerate collections; done means establishing whether a unified .vcf export is supported and documenting the required behavior, or defining the feature scope and tests if it is not.