Refactor signer pruning with upkeep service

[sfauvel]

Content

This PR remove the pruning from the save function and use the upkeep service instead.
The StakeStore is moved from persistence to signer.
The EpochPruningTask is implemented over the StorePruner in the Signer for the ProtocolInitializerStore and StakeStore.

Pre-submit checklist

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

Issue(s)

Closes #2075

[github-actions]

Test Results

    4 files  ±0     51 suites  ±0   11m 5s ⏱️ +21s
1 441 tests ±0  1 441 ✅ ±0  0 💤 ±0  0 ❌ ±0 
1 652 runs  ±0  1 652 ✅ ±0  0 💤 ±0  0 ❌ ±0 

Results for commit d9ca627. ± Comparison against base commit 0a7fb9f.

This pull request removes 7 and adds 7 tests. Note that renamed tests count towards both.

mithril-persistence ‑ store::stake_store::tests::check_retention_limit
mithril-persistence ‑ store::stake_store::tests::get_stakes_for_empty_epoch
mithril-persistence ‑ store::stake_store::tests::get_stakes_for_existing_epoch
mithril-persistence ‑ store::stake_store::tests::retrieve_returns_stake_distribution
mithril-persistence ‑ store::stake_store::tests::retrieve_with_no_stakes_returns_none
mithril-persistence ‑ store::stake_store::tests::save_key_in_empty_store
mithril-persistence ‑ store::stake_store::tests::update_signer_in_store

mithril-signer ‑ store::stake_store::tests::check_retention_limit
mithril-signer ‑ store::stake_store::tests::get_stakes_for_empty_epoch
mithril-signer ‑ store::stake_store::tests::get_stakes_for_existing_epoch
mithril-signer ‑ store::stake_store::tests::retrieve_returns_stake_distribution
mithril-signer ‑ store::stake_store::tests::retrieve_with_no_stakes_returns_none
mithril-signer ‑ store::stake_store::tests::save_key_in_empty_store
mithril-signer ‑ store::stake_store::tests::update_signer_in_store

♻️ This comment has been updated with latest results.

[jpraynaud]

LGTM 👍

[Alenar]

LGTM

[dlachaume]

LGTM 🚀