add missing attributes for per unit view

[EtienneLt]

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[EtienneLt]

Did you check that all attributes that are now accessible are correctly per-united? For example target_v for transformer 2 and 3, shunt ? Also all target p and q (hvdc lines etc ) ?

I will add some tests

[EtienneLt]

Did you check that all attributes that are now accessible are correctly per-united? For example target_v for transformer 2 and 3, shunt ? Also all target p and q (hvdc lines etc ) ?

well all targetv for transformer and target p ans q for hvdc are default attributes so they were already perunit I added the non default attributes for generators and vsc stations (max_q_at_p, ....)

[EtienneLt]

update_ratio_tap_changers is missing