Replace instances of .to(unit).value with .to_value(unit)

Once #6127 is merged, we should replace any instances of .to(unit).value in code or documentation to .to_value(unit) as it will be faster.

Hm, I labeled this units but actually it touches many of the subpackages because it is a large find-and-replace...

Okay, I removed units and added docs.

Ok -- it applies mostly to code, but there are a few instances in the docs as well.

Oops, I had already done this in the other PR. Will make a new one just for the replacement...

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