Importbot treats volumes of series as editions

Importbot imports volumes of series as editions of the same work. This is time consuming to fix as each edition record must be manually split and have the author assigned.

### Evidence / Screenshot (if possible)
https://openlibrary.org/works/OL26543324W/Theme_Sets._Ice
### Relevant url?

https://openlibrary.org/works/OL26543324W/Theme_Sets._Ice
### Steps to Reproduce

1. Go to ...
2. Do ...

* Actual:
* Expected:

### Details

- **Logged in (Y/N)?**
- **Browser type/version?**
- **Operating system?**
- **Environment (prod/dev/local)?** prod

### Proposal & Constraints

Import each volume as an independent work.
### Related files

### Stakeholders

@mekarpeles

Start by examining Importbot's handling of the linked Theme Sets: Ice work record and reproducing how its series volumes become editions of one work. Confirm the intended result against the proposal: each volume should be imported as an independent work, with its author assigned, and existing records should no longer require manual splitting.

Written by the indexing model from the issue text.