fix: workflow definition initialization race

[rustatian]

Reason for This PR

• RPC panic if the Replay method was called before the plugin was initialized but after RPC was opened.

Description of Changes

• Fix workflow definition panic.
• Refactoring.

License Acceptance

By submitting this pull request, I confirm that my contribution is made under the terms of the MIT license.

PR Checklist

[Author TODO: Meet these criteria.] [Reviewer TODO: Verify that these criteria are met. Request changes if not]

• [x] All commits in this PR are signed (git commit -s).
• [x] The reason for this PR is clearly provided (issue no. or explanation).
• [x] The description of changes is clear and encompassing.
• [x] Any required documentation changes (code and docs) are included in this PR.
• [x] Any user-facing changes are mentioned in CHANGELOG.md.
• [x] All added/changed functionality is tested.

[codecov-commenter]

Codecov Report

Patch and project coverage have no change.

Comparison is base (2700a47) 22.67% compared to head (ec45e21) 22.67%.

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Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #418 +/- ## ======================================= Coverage 22.67% 22.67% ======================================= Files 4 4 Lines 269 269 ======================================= Hits 61 61 Misses 206 206 Partials 2 2 ```

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