Singleton import with tracks marked as compilation not treated as singleton

### Problem

When importing singletons using `beet -s`, if the file has a compilation tag, it is not treated as a singleton.
It is saved using the comp rather than singleton naming.

```
> beet -vv import -s Classical/Johannes_Brahms_-_Hungarian_Dance_No_5_In_G_Minor.mp3
user configuration: /home/user/.config/beets/config.yaml
data directory: /home/user/.config/beets
plugin paths:
lastgenre: Loading canonicalization tree /usr/share/beets/beetsplug/lastgenre/genres-tree.yaml
Sending event: pluginload
library database: /home/user/.beets/library.blb
library directory: /home/user/.beets/music
Sending event: library_opened
Sending event: import_begin
Sending event: import_task_created
/var/temp/Clean/Classical/Johannes_Brahms_-_Hungarian_Dance_No_5_In_G_Minor.mp3
0 of 1 items replaced
Sending event: database_change
Sending event: database_change
lastgenre: added last.fm item genre (artist): Classical
Sending event: database_change
Sending event: item_linked
Sending event: database_change
Sending event: database_change
Sending event: import_task_files
Sending event: item_imported
Sending event: import
Sending event: cli_exit
```

### Setup

* OS: Debian 12.4 amd64
* Python version: 3.11.2
* beets version: 1.6.0

Reproduce the issue with the provided `beet -vv import -s` command and an audio file carrying a compilation tag. Trace the singleton import path and compare the resulting compilation-based name with the expected singleton naming; done means singleton imports retain singleton naming even when the track is marked as a compilation.

Written by the indexing model from the issue text.