Feat: Smartplaylist: Add dest_regen option for regenerating destination path

[pierreay]

Problem

1. When items are imported into the library in a don't copy-move mode (-C -M options), they will be registered inside the Beets database using their original paths. However, during subsequent processing (e.g., a convert operation), a path following the Beets path format can be generated.
2. When generating playlists using smartplaylist plugin, only the path registered inside the Beets database (the original path) can be use inside the output playlist. This block the compatibility with other plugins.

Solution

I added a a new optional configuration option known as dest_regen (as well as its equivalent dest-regen on the CLI) to regenerate items' path in the generated playlist instead of using the ones of the library, just like a convert or a move operation would have done. This operation will happen before the relative_to and prefix options, which makes sense to do so and not in another order, otherwise this new option (dest_regen)) would overwrite the desired behavior of the other mentioned options (relative_to and prefix). It is then helpful to generate playlists compatible with the convert plugin.

To Do

• Documentation
• Changelog
• Tests. (I may write one in the future if this PR is considered)

[Copilot]

Pull Request Overview

This PR adds a new configuration option "dest_regen" (with its CLI alias "--dest-regen") to support regenerating the destination path for playlist items, thereby improving compatibility with the convert plugin.

• Introduces a configuration flag "dest_regen" with a default of False.
• Adds a corresponding CLI option "--dest-regen".
• Updates the playlist update logic to optionally use the item's regenerated destination path.

Files not reviewed (2)

• docs/changelog.rst: Language not supported
• docs/plugins/smartplaylist.rst: Language not supported

Comments suppressed due to low confidence (1)

beetsplug/smartplaylist.py:267

• The new dest_regen functionality is not covered by tests; please add tests to ensure that the regenerated destination path is correctly handled under various configurations.

dest_regen = self.config["dest_regen"].get()

[pierreay]

Hello @snejus ! :) Rebasing on master and writing of a test to test the dest_regen feature logic is done!