fix: affine unit promotion in ustrip

[MilesCranmer]

No description provided.

[github-actions]

Benchmark Results

	main	a4df72b...	main / a4df72b...
Quantity/creation/Quantity(x)	2.79 ± 0.001 ns	4.02 ± 0.91 ns	0.696
Quantity/creation/Quantity(x, length=y)	3.43 ± 0.01 ns	3.43 ± 0.01 ns	1
Quantity/with_numbers/*real	3.41 ± 0.01 ns	3.11 ± 0.001 ns	1.1
Quantity/with_numbers/^int	8.68 ± 1.6 ns	8.68 ± 1.6 ns	1
Quantity/with_numbers/^int * real	8.99 ± 1.8 ns	8.99 ± 1.6 ns	1
Quantity/with_quantity/+y	4.04 ± 0.011 ns	4.35 ± 0.01 ns	0.929
Quantity/with_quantity//y	3.11 ± 0.001 ns	3.11 ± 0.001 ns	1
Quantity/with_self/dimension	3.1 ± 0.01 ns	3.11 ± 0.01 ns	1
Quantity/with_self/inv	3.41 ± 0.01 ns	3.11 ± 0.001 ns	1.1
Quantity/with_self/ustrip	2.79 ± 0.01 ns	2.79 ± 0.01 ns	1
QuantityArray/broadcasting/multi_array_of_quantities	0.0874 ± 0.0013 ms	0.0874 ± 0.0013 ms	1
QuantityArray/broadcasting/multi_normal_array	0.0497 ± 0.0022 ms	0.0528 ± 0.0006 ms	0.941
QuantityArray/broadcasting/multi_quantity_array	0.053 ± 0.00041 ms	0.0591 ± 0.0063 ms	0.896
QuantityArray/broadcasting/x^2_array_of_quantities	15.1 ± 7.9 μs	15.2 ± 5.7 μs	0.993
QuantityArray/broadcasting/x^2_normal_array	2.48 ± 1.7 μs	2.69 ± 2.2 μs	0.922
QuantityArray/broadcasting/x^2_quantity_array	6.48 ± 0.16 μs	3.55 ± 0.47 μs	1.83
QuantityArray/broadcasting/x^4_array_of_quantities	0.0842 ± 0.0012 ms	0.0813 ± 0.0011 ms	1.04
QuantityArray/broadcasting/x^4_normal_array	0.0497 ± 0.0024 ms	0.0497 ± 0.00025 ms	1
QuantityArray/broadcasting/x^4_quantity_array	0.0498 ± 0.00037 ms	0.0529 ± 0.00034 ms	0.942
time_to_load	0.201 ± 0.0016 s	0.202 ± 0.0029 s	0.998

Benchmark Plots

A plot of the benchmark results have been uploaded as an artifact to the workflow run for this PR.
Go to "Actions"->"Benchmark a pull request"->[the most recent run]->"Artifacts" (at the bottom).