chore: workflow refactoring

[rustatian]

Reason for This PR

• WorkflowDefinition refactoring

Description of Changes

• Move LocalActivityFn to the separate structure
• Protect MessageQueue with mutex
• Add more logs

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]

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

[codecov-commenter]

Codecov Report

Merging #307 (bd7daf3) into master (b06b5cc) will increase coverage by 0.53%.
The diff coverage is 7.46%.

@@            Coverage Diff            @@
##           master    #307      +/-   ##
=========================================
+ Coverage    3.17%   3.70%   +0.53%     
=========================================
  Files          18      19       +1     
  Lines        1605    1645      +40     
=========================================
+ Hits           51      61      +10     
- Misses       1552    1582      +30     
  Partials        2       2              

Impacted Files	Coverage Δ
aggregatedpool/activity.go	0.00% <0.00%> (ø)
aggregatedpool/handler.go	0.00% <0.00%> (ø)
aggregatedpool/local_activity.go	0.00% <0.00%> (ø)
aggregatedpool/workflow.go	0.00% <0.00%> (ø)
plugin.go	0.00% <0.00%> (ø)
queue/queue.go	78.57% <100.00%> (+6.69%)	⬆️

Help us with your feedback. Take ten seconds to tell us how you rate us. Have a feature suggestion? Share it here.