docs: update batch job execution description to the new design

[evacchi]

Why is this PR needed?

#581 and #584 introduced changes that are no longer reflected in the documentation

What does this PR do?

Update the stale design docs with the changes introduced in #581 and #584

How was this tested?

• Unit tests added/updated/verified
• Integration/e2e tests added/updated/verified
• Manual testing performed

Checklist

• Commits are signed off (git commit -s) per DCO
• Code follows project contributing guidelines
• CI checks pass (make ci)
• E2E tests pass (make test-e2e)

Related Issues

#581 and #584

[Copilot]

Pull request overview

Updates the batch gateway design documentation to reflect the channel-based execution pipeline introduced in #581/#584, clarifying how sync vs async dispatch are realized as different leaf dispatchers in the same pipeline and updating the llm-d-async queue naming/consumption description accordingly.

Changes:

• Refreshes the batch dispatcher queue design doc to match the current async integration (AsyncDispatcher leaf, broadcaster-based result fanout, suffix-less result queue naming).
• Updates the batch processor architecture doc to describe the new channel-based pipeline actors (RequestSource → dispatcher chain → ResultCollector) and revised scheduling/concurrency semantics.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
docs/design/batch-dispatcher-queue-design.md	Updates async queue naming and result-consumption design to match the new pipeline-based implementation.
docs/design/batch_processor_architecture.md	Reworks the execution/scheduling sections to document the channel-based pipeline design introduced in #581/#584.

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[j-mok-dev]

lgtm. I see that this PR still documents the 4-context model, but #625 changes it to a single abort context with batchctx.Cause. Maybe we can merge #625 first then rebase this PR, and update the Context Hierarchy section again with the batchctx-based context.

[evacchi]

agreed!

[evacchi]

the text now includes the description of the changes detailed in #625, so it should be merged after that.

[github-actions]

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