Global optimization

We probably need to modify `dask.base` to call some dask-expr `optimize` function. We probably also want to call this on everything we're computing all at once.

Start by reading dask.base and locating the dask-expr optimize function mentioned in the issue. Trace how computations are submitted and determine the expected behavior when everything is computed at once; done means the global optimization path is integrated and covered by the relevant tests, though no test file is named here.

Written by the indexing model from the issue text.