[allison-truhlar]

What changed

Views now pick layer types the same way the standalone Neuroglancer
button does:

• OME-Zarr datasets use the thumbnail-edge heuristic from the
  single-dataset preview to choose between image and segmentation.
  The disableHeuristicalLayerTypeDetection preference turns it off,
  as it does for the standalone button.
• Plain Zarr arrays always open as image. The standalone button
  has no thumbnail to run the heuristic on, so it does the same. This
  removes the name-and-dtype guess in guessPlainLayerType.

Two follow-on changes keep checkout fast and reliable now that it
renders thumbnails:

• buildViewState starts every dataset at once instead of awaiting
  them one at a time, so checkout time no longer grows with cart size.
• useCreateViewFlow opens the draft tab right away on click, then
  sends the tab to the draft once the state is built. Rendering the
  thumbnails can take longer than the click's user activation lasts,
  and then the browser blocks the popup. If building the state fails,
  the tab closes.

Why

The metadata panel and the standalone Neuroglancer button could call a
dataset a segmentation while the View opened it as an image, or the
other way around.

Addresses Clickup ids 17tkuw61tnm and 17tkuw629cv

Testing

• New unit tests in viewCheckout.test.ts cover inference on, inference
  off, and the parameter it passes through.
• useCreateViewFlow.test.tsx checks that the pre-opened tab gets the
  draft URL and closes on failure.
• pixi run test-frontend passes for viewCheckout, useAddToView,
  useCartCheckout, and useCreateViewFlow.
• Checked out a segmentation dataset by hand and confirmed the View
  opens it as a segmentation layer.

@krokicki