Support adapt on closures with boxes.

[maleadt]

Fixes https://github.com/JuliaGPU/Adapt.jl/issues/57

[codecov[bot]]

Codecov Report

Base: 84.12% // Head: 83.58% // Decreases project coverage by -0.55% :warning:

Coverage data is based on head (87e5a75) compared to base (bb41a7e). Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #58 +/- ## ========================================== - Coverage 84.12% 83.58% -0.55% ========================================== Files 5 5 Lines 63 67 +4 ========================================== + Hits 53 56 +3 - Misses 10 11 +1 ``` | [Impacted Files](https://codecov.io/gh/JuliaGPU/Adapt.jl/pull/58?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=JuliaGPU) | Coverage Δ | | |---|---|---| | [src/base.jl](https://codecov.io/gh/JuliaGPU/Adapt.jl/pull/58?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=JuliaGPU#diff-c3JjL2Jhc2Uuamw=) | `93.33% <100.00%> (+2.42%)` | :arrow_up: | | [src/wrappers.jl](https://codecov.io/gh/JuliaGPU/Adapt.jl/pull/58?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=JuliaGPU#diff-c3JjL3dyYXBwZXJzLmps) | `72.22% <0.00%> (-2.78%)` | :arrow_down: | Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=JuliaGPU). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=JuliaGPU)

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