Refactor to CanvasBuilder further to make prompt logging easier [#3556264]

I don't have all the context this but we looking at prompt logging. Everything current runs through \Drupal\canvas_ai\Controller\CanvasBuilder::render which currently 242 lines after #3555464: CanvasBuilder::render() logic around specific tool response is unclear this will a bit shorter but it still does a ton.

Simplify \Drupal\canvas_ai\Controller\CanvasBuilder::render
Start with 1 MR to clean up what is there so adapting it for logging will be easier

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3556264-refactor-to-canvasbuilder changes, plain diff MR !297
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