Add `webers`, `henry`, and `siemens`

[ven-k]

These are quite commonly used units and will be useful to house them in here.

I didn't see any testset for derived units. LMK if & how I should add tests for these four.

[github-actions[bot]]

Benchmark Results

	main	7de3150917a61c...	t[main]/t[7de3150917a61c...]
Quantity/creation/Quantity(x)	2.79 ± 0.009 ns	3.72 ± 0.86 ns	0.752
Quantity/creation/Quantity(x, length=y)	3.42 ± 0.01 ns	3.42 ± 0.01 ns	1
Quantity/with_numbers/*real	3.1 ± 0.01 ns	3.11 ± 0.01 ns	1
Quantity/with_numbers/^int	8.05 ± 1.8 ns	8.36 ± 2.2 ns	0.964
Quantity/with_numbers/^int * real	8.36 ± 1.9 ns	8.05 ± 1.9 ns	1.04
Quantity/with_quantity/+y	4.04 ± 0.001 ns	4.04 ± 0.001 ns	1
Quantity/with_quantity//y	3.11 ± 0.001 ns	3.11 ± 0.009 ns	1
Quantity/with_self/dimension	3.1 ± 0.01 ns	2.79 ± 0.009 ns	1.11
Quantity/with_self/inv	3.11 ± 0.001 ns	3.11 ± 0.001 ns	1
Quantity/with_self/ustrip	2.79 ± 0 ns	2.79 ± 0.01 ns	1
QuantityArray/broadcasting/multi_array_of_quantities	0.145 ± 0.00094 ms	0.15 ± 0.0011 ms	0.965
QuantityArray/broadcasting/multi_normal_array	0.0528 ± 0.00016 ms	0.0498 ± 0.00016 ms	1.06
QuantityArray/broadcasting/multi_quantity_array	0.158 ± 0.00037 ms	0.155 ± 0.00067 ms	1.02
QuantityArray/broadcasting/x^2_array_of_quantities	22.4 ± 1.5 μs	22.8 ± 1.5 μs	0.982
QuantityArray/broadcasting/x^2_normal_array	3.95 ± 1 μs	4.21 ± 0.86 μs	0.938
QuantityArray/broadcasting/x^2_quantity_array	6.92 ± 0.22 μs	6.92 ± 0.22 μs	1
QuantityArray/broadcasting/x^4_array_of_quantities	0.0786 ± 0.00045 ms	0.0783 ± 0.00035 ms	1
QuantityArray/broadcasting/x^4_normal_array	0.0498 ± 0.00015 ms	0.0497 ± 0.00015 ms	1
QuantityArray/broadcasting/x^4_quantity_array	0.0499 ± 0.00013 ms	0.0499 ± 0.00013 ms	1
time_to_load	0.132 ± 0.0003 s	0.133 ± 0.00085 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).

[MilesCranmer]

I'm happy with the others but radians are really tricky and are probably best left for later.

[MilesCranmer]

For example, what should sind(1u"rad") do? Right now with this PR it would evaluate as the sinusoid of 1 degree, even though it was clearly written as 1u"rad"... So basically needs a lot of work to get right.

[MilesCranmer]

Thanks for the PR!! 🚀