handle unitful infinite arguments

[stevengj]

Closes #64.

[codecov[bot]]

Codecov Report

Base: 97.86% // Head: 97.59% // Decreases project coverage by -0.28% :warning:

Coverage data is based on head (44eb040) compared to base (d4e1c58). Patch coverage: 95.00% of modified lines in pull request are covered.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #65 +/- ## ========================================== - Coverage 97.86% 97.59% -0.28% ========================================== Files 5 5 Lines 328 332 +4 ========================================== + Hits 321 324 +3 - Misses 7 8 +1 ``` | [Impacted Files](https://codecov.io/gh/JuliaMath/QuadGK.jl/pull/65?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=JuliaMath) | Coverage Δ | | |---|---|---| | [src/adapt.jl](https://codecov.io/gh/JuliaMath/QuadGK.jl/pull/65?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=JuliaMath#diff-c3JjL2FkYXB0Lmps) | `98.00% <95.00%> (-0.96%)` | :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=JuliaMath). 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=JuliaMath)

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[stevengj]

Would be good to add Unitful as a test dependency so that we can check for regressions.

[sostock]

Maybe we should revive https://github.com/JuliaLang/julia/pull/39852 so that QuadGK and other packages can avoid adding a Unitful test dependency in the future.