Test forced snapshots while service is opening

[achamayou]

Summary

• add an e2e regression test that leaves the service in Opening
• accept trigger_snapshot through governance and advance commits with governance transactions
• require both the snapshot and its ledger chunk to be committed on disk

Testing

• python -m black --check tests/e2e_operations.py
• python -m ruff check tests/e2e_operations.py
• python -m py_compile tests/e2e_operations.py

Closes #6469

[Copilot]

Pull request overview

This PR adds an end-to-end regression test to ensure that forcing a snapshot via governance while the service remains in Opening results in both (a) a committed snapshot file and (b) a committed ledger chunk containing that snapshot—covering the failure described in #6469.

Changes:

• Add test_forced_snapshot_while_opening which triggers a snapshot via governance while the service is still Opening, then verifies the snapshot exists and the containing ledger chunk is committed/complete.
• Add a dedicated runner (run_forced_snapshot_while_opening) that starts a network without opening it, executes the regression test, and is invoked from run().

Custom instructions used:

• .github/copilot-instructions.md
• .github/instructions/reviewing.instructions.md