Unified set() for magnets

[gubaidulinvadim]

Description, motivation and use case
Currently, for all magnets you can work in strengths or currents. One could wish to always work with a default unit and have a shorter magnet.set() instread of magnet.strength.set().

Proposed solution
The proposal is to have

• default choice (strengths or currents)
• .set() that will shortcut to strength.set() or currents.set() depending on the default
• After Simple unit convertion to SI on set() #350 is solved .set() can accept a pint.Quantity with a unit and based on the unit use strengths or currents.

Additional context
Some cases with combined function magnets may not be trivial.

Checklist

• I've assigned this issue to a project
• I've @-mentioned relevant people