fix(rust/cardano-chain-follower): fix immutable roll forward events

[stevenj]

Description

Fixes generation of Immutable Chain Roll Forward events.

Related Issue(s)

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e.g., Closes #123, Resolves #456 Fixes #367

Description of Changes

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Breaking Changes

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Related Pull Requests

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Please confirm the following checks

• My code follows the style guidelines of this project
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream module

[github-actions]

✅ Test Report | ${\color{lightgreen}Pass: 309/309}$ | ${\color{red}Fail: 0/309}$ |