fix: fix spo journey test

[ladamesny]

Description

Fix SPO journey tests and auto-calculate init_timestamp

What Changed
• Auto-calculate init_timestamp: Dynamically calculate based on current network state instead of hardcoding, eliminating manual config updates after network restarts
• Fix epoch mapping errors: Handle None returns from find_mc_epoch() to prevent TypeError crashes
• Fix participation validation: Properly remove all entries per producer (not just one) since participation data contains multiple entries with different block counts

link
to the issue.

Checklist

• Commit sequence broadly makes sense and commits have useful messages.
• The size limit of 400 LOC isn't needlessly exceeded
• The PR refers to a JIRA ticket (if one exists)
• New tests are added if needed and existing tests are updated.
• New code is documented and existing documentation is updated.
• Relevant logging and metrics added
• Any changes are noted in the changelog.md for affected crate
• Self-reviewed the diff