Spotify Audio Features API is deprecated

### Problem

The Spotify plugin cannot populate audio features because Spotify has deprecated the audio features API:

https://developer.spotify.com/blog/2024-11-27-changes-to-the-web-api

The new Reccobeats API has an audio features endpoint:

https://reccobeats.com/docs/apis/get-audio-features

I've tested it and it seems to work. I don't know how it compares to the Spotify API.

Reccobeats also has an analysis endpoint that will extract audio features from an audio clip:

https://reccobeats.com/docs/apis/extract-audio-features

I don't know how stable the Reccobeats API is. I can't find any information about the developer, but the changelog is active as of August 2025:

https://reccobeats.com/docs/changelog

It might be worth adding a Reccobeats plugin to populate or generate audio features.

### Setup

* OS:
* Python version:
* beets version:
* Turning off plugins made problem go away (yes/no):

My configuration (output of `beet config`) is:

```yaml
(paste here)
```