Fix aggregator stress test

[dlachaume]

Content

This PR fixes an issue with the aggregator stress test by implementing the following changes:

• Replace the default value for mithril-era from thales to pythagoras.
• Adapt computed protocol messages to include the required message parts: NextAggregateVerificationKey and NextProtocolParameters.

Additionally, the default value for mithril-era in the end-to-end tests has been updated from thales to pythagoras.

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Note: These modifications affect the execution time of the aggregator stress test due to the increased size of the messages that need to be signed. Since the aggregator stress test is mainly triggered by a nightly workflow, the impact should be minimal.

Before:
Number of concurrent signers: 500
Number of concurrent clients: 1000
Average execution duration: 3min30s

With the modifications:
Number of concurrent signers: 500
Number of concurrent clients: 1000
Average execution duration: 9min10s

Pre-submit checklist

• Branch
  • Crates versions are 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

Issue(s)

Closes #2299

[github-actions]

Test Results

    4 files  ±0     56 suites  ±0   21m 34s ⏱️ +35s
1 596 tests ±0  1 596 ✅ ±0  0 💤 ±0  0 ❌ ±0 
1 900 runs  ±0  1 900 ✅ ±0  0 💤 ±0  0 ❌ ±0 

Results for commit fadb6c8. ± Comparison against base commit 38a7584.

♻️ This comment has been updated with latest results.

[jpraynaud]

LGTM 👍