We can't properly deal with delayed inputs

Every argument could theoretically be a delayed object, similar to how every argument could be a dask-expr collection, we can't deal with this yet since we never check for them

I created a *very* naive implementation of a delayed expression ``_Delayed`` to capture some things, but we should think critically about it before moving ahead with this issue.

I suggest that we unpack delayed object similar to what we do with collections, in the constructor of ``Expr``

Start by reviewing the Expr constructor and the existing collection-unpacking behavior, then inspect the naive _Delayed implementation described in the issue. Clarify how delayed arguments should be represented and handled before changing the implementation; done means delayed inputs are dealt with consistently across expression construction.

Written by the indexing model from the issue text.