Make Europeana fetch viable

## Problem
The Europeana data set is too big to fetch all at once, or in its entirety.
- data providers: 4206
- rights: 64

Assuming approximately 1 second per query, the expected duration is approximately 75 hours.

## Description
1. Add counts for rights only (not including data providers)
2. Write a query plan on first run per quarter to map out which queries to make over 30 runs (30 days)

## Alternatives
Parallel queries (probably considered impolite, Timid Robot will ask)

## Additional context
- https://github.com/creativecommons/quantifying/blob/main/sources.md#europeana

## Implementation

- [ ] I would be interested in implementing this feature.

Start with the Europeana section linked from sources.md and trace the existing Europeana fetch entry point and query-counting flow. Define how rights-only counts and a first-run quarterly plan should cover 30 runs over 30 days, then verify that the resulting schedule avoids fetching the full dataset at once.

Scritto dal modello di indicizzazione a partire dal testo della issue.