Adds recastCofree

[mikesol]

Description of the change

Recast cofree is useful in cases where one wants to change the functor of a Cofree but the natural transformation f ~> g required in hoistCofree is too restrictive. This allows g to peek on the inside of f (Cofree f a).

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Checklist:

• Added the change to the changelog's "Unreleased" section with a reference to this PR (e.g. "- Made a change (#0000)")
• Linked any existing issues or proposals that this pull request should close
• Updated or added relevant documentation
• Added a test for the contribution (if applicable)