Ensure user-defined mutable version of dimensions always copied

[MilesCranmer]

While the default Dimensions is immutable, and the mutable SymbolicDimensions (which uses a sparse array) should always create a copy anyways, the user could declare a AbstractDimensions that is mutable and does not copy itself.

Therefore this PR implements copy for a variety of operations on both QuantityArray and AbstractQuantity.

todo:

• turn off copies for broadcasting interface

[github-actions]

Benchmark Results

	main	5679cd6...	t[main]/t[5679cd6...]
Quantity/creation/Quantity(x)	3.2 ± 0.1 ns	3.2 ± 0.1 ns	1
Quantity/creation/Quantity(x, length=y)	3.7 ± 0.1 ns	3.7 ± 0.1 ns	1
Quantity/with_numbers/*real	3.2 ± 0.1 ns	3.2 ± 0.1 ns	1
Quantity/with_numbers/^int	10.1 ± 2.5 ns	10.1 ± 2.4 ns	1
Quantity/with_numbers/^int * real	10.5 ± 2.5 ns	10.5 ± 2.5 ns	1
Quantity/with_quantity/+y	6 ± 0.2 ns	5.9 ± 0.1 ns	1.02
Quantity/with_quantity//y	3.7 ± 0.1 ns	3.7 ± 0.1 ns	1
Quantity/with_self/dimension	1.6 ± 0.1 ns	1.6 ± 0.1 ns	1
Quantity/with_self/inv	3.3 ± 0.1 ns	3.3 ± 0.1 ns	1
Quantity/with_self/ustrip	1.6 ± 0.1 ns	1.6 ± 0.1 ns	1
QuantityArray/broadcasting/multi_array_of_quantities	0.198 ± 0.026 ms	0.2 ± 0.0055 ms	0.993
QuantityArray/broadcasting/multi_normal_array	0.0684 ± 0.001 ms	0.0686 ± 0.001 ms	0.997
QuantityArray/broadcasting/multi_quantity_array	0.232 ± 0.0029 ms	0.232 ± 0.0033 ms	1
QuantityArray/broadcasting/x^2_array_of_quantities	0.0415 ± 0.0033 ms	0.0498 ± 0.0035 ms	0.833
QuantityArray/broadcasting/x^2_normal_array	8.8 ± 1.1 μs	10 ± 1.1 μs	0.88
QuantityArray/broadcasting/x^2_quantity_array	10.7 ± 0.7 μs	11 ± 1.1 μs	0.973
QuantityArray/broadcasting/x^4_array_of_quantities	0.117 ± 0.0033 ms	0.122 ± 0.0043 ms	0.956
QuantityArray/broadcasting/x^4_normal_array	0.0585 ± 0.0034 ms	0.0624 ± 0.0008 ms	0.938
QuantityArray/broadcasting/x^4_quantity_array	0.0854 ± 0.0041 ms	0.0827 ± 0.004 ms	1.03
time_to_load	0.166 ± 0.00029 s	0.17 ± 0.0018 s	0.975

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).

[MilesCranmer]

Superseded by #56