feat: use unique ProtocolInitializer per epoch in signer

[jpraynaud]

Content

This PR includes the creation of a single ProtocolInitializer for a signer for each epoch, when a new one used to be created each time the signer was restarted.

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• Branch
  • Tests are provided (if possible)
  • Crates versions are updated (if relevant)
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Issue(s)

Closes #2424

[Copilot]

Pull Request Overview

This PR modifies the signer to maintain a unique ProtocolInitializer per epoch, preventing the creation of new initializers on each signer restart while ensuring the same one is used throughout the epoch's lifetime.

• Changed from "insert or replace" to "insert or ignore" database operations to prevent overwriting existing protocol initializers
• Added test coverage to verify protocol initializers are only created once per epoch and never updated
• Moved protocol initializer storage to occur before signer registration to ensure retrieval works correctly

Reviewed Changes

Copilot reviewed 5 out of 6 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
mithril-signer/src/runtime/runner.rs	Reorders protocol initializer storage before signer registration and adds retrieval logic
mithril-signer/src/database/tests/protocol_initializer.rs	Adds test to verify protocol initializers are created once per epoch and improves test data uniqueness
mithril-signer/src/database/repository/protocol_initializer_repository.rs	Changes from InsertOrReplace to InsertOrIgnore query to prevent overwriting
mithril-signer/src/database/query/protocol_initializer/insert_protocol_initializer.rs	Renames and updates query from "insert or replace" to "insert or ignore"
mithril-signer/Cargo.toml	Bumps version from 0.2.271 to 0.2.272

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[github-actions]

Test Results

    4 files  ±0    168 suites  ±0   23m 5s ⏱️ -24s
2 228 tests +1  2 228 ✅ +1  0 💤 ±0  0 ❌ ±0 
6 881 runs  +2  6 881 ✅ +2  0 💤 ±0  0 ❌ ±0 

Results for commit 7c76a0d. ± Comparison against base commit 046a4f8.

♻️ This comment has been updated with latest results.

[turmelclem]

LGTM 👍