feat: add observable queue

[amondnet]

Describe the changes proposed in this Pull Request.

Fixes #887

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Pull Request Checklist

• If the changes are being made to code, ensure the version in pubspec.yaml is updated.
• Increment the major/minor/patch/patch-count, depending on the complexity of change
• Add the necessary unit tests to ensure the coverage does not drop
• Update the Changelog to include all changes made in this PR, organized by version
• Run the melos run set_version command from the root directory
• Include the necessary reviewers for the PR
• Update the docs if there are any API changes or additions to functionality