- **task: Start refactoring shell builder**
- **Unify Windows implementation of shell builder so that it's treated
like any other kind of a "custom" shell.**
- **Rename task/lib.rs to task/task.rs**

Release Notes:

- N/A

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Co-authored-by: Remco Smits <djsmits12@gmail.com>
Co-authored-by: Anthony Eid <hello@anthonyeid.me>