BE-455: HashQL: Introduce evaluation orchestrator #8586

This check will pass when downstack PRs merge

#8675 needs to be merged into main before you can merge this PR.
- This PR is stacked on top of #8675. Merging this PR on GitHub will cause it to merge incorrectly into #8675 instead of main.
- Learn more about stacked PRs here
To ensure that these PRs merge correctly, view and merge this PR with Graphite
To disable this check, edit your organization's settings on Graphite.