feat(editor): Always keep at least one executing node indicator in the workflow

[alexgrozav]

Summary

Added a node execution queue that ensures there's always at least one node executing in the workflow until it finishes.

When emitting nodeExecuteBefore and nodeExecuteAfter socket events, the data serialization function is too slow when dealing with large amounts of data. This causes events to be delayed and we end up in a state where the previous node has finished and the new node event takes a while to start, therefore there's no node currently executing. This leads users to believe the workflow is stuck or finished.

Related Linear tickets, Github issues, and Community forum posts

https://linear.app/n8n/issue/CAT-324/bug-spinner-doesnt-show-up-on-executing-nodes

Review / Merge checklist

• PR title and summary are descriptive. (conventions)
• Docs updated or follow-up ticket created.
• Tests included.
• PR Labeled with release/backport (if the PR is an urgent fix that needs to be backported)

[codecov]

Codecov Report

Attention: Patch coverage is 94.44444% with 1 line in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
packages/editor-ui/src/stores/workflows.store.ts	94.44%	1 Missing ⚠️

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