Default fetch cursor value function fails when base schema has the same field has the binding's

[tanguilp]

I have a cursor with 2 fields, one being a preload, something like: [{:author, :name}, :name] (let's say the base schema is :post).

I think the default fetch cursor value erroneously tries to fetch first the field on the base schema: https://github.com/duffelhq/paginator/blob/main/lib/paginator.ex#L243

As a result, if the base schema and the preloaded schema have the same field, then the wrong field from the base schema is used.

In the example above, that would result in the cursor having twice the post's name:

%{:id => 92575, :name => "Post's name", {:author, :name} => "Post's name"}

instead of

%{:id => 92575, :name => "Post's name", {:author, :name} => "Author's name"}

If I've not misunderstood how this library works, I'm ready to provide with a PR!