Feat: record informations in epoch service for status route

[dlachaume]

Content

This PR includes storing all the necessary information in the EpochService to support the future /status route on the aggregator.

The following data is now saved:

• Current Cardano era
• Current Mithril era
• Total number of SPOs for the current epoch
• Total stake for the current epoch

This PR will allow the /status route to expose these details when implemented.

Pre-submit checklist

• Branch
  • [x] Tests are provided (if possible)
  • [x] Crates versions are updated (if relevant)
  • [ ] CHANGELOG file is updated (if relevant)
  • [x] Commit sequence broadly makes sense
  • [x] Key commits have useful messages
• PR
  • [x] No clippy warnings in the CI
  • [x] Self-reviewed the diff
  • [x] Useful pull request description
  • [x] Reviewer requested
• Documentation
  • [ ] Update README file (if relevant)
  • [ ] Update documentation website (if relevant)
  • [ ] Add dev blog post (if relevant)

Issue(s)

Relates to #2071

[github-actions[bot]]

Test Results

    4 files  ±0     51 suites  ±0   11m 2s ⏱️ -10s 1 437 tests +1  1 437 ✅ +1  0 💤 ±0  0 ❌ ±0  1 648 runs  +1  1 648 ✅ +1  0 💤 ±0  0 ❌ ±0 

Results for commit b4f4c4fd. ± Comparison against base commit d2d8c4cd.

:recycle: This comment has been updated with latest results.