You might be right about this. I found no mention of this at all in the Norwegian constitution, and I found various clauses explicitly giving immunity for votes cast during their tenure in several other constitutions I looked at. This presumably also applies to laws later ruled unconstitutional.

It is not what I would have expected, and strikes me as an oversight. Moreover, it reeks of entitlement.

There should never be any necessity to pass laws that even come close to violating a constitution, so no, I do not believe it would slow down the legislative process.

Instead, it would provide an incentive to avoid passing laws which will hopefully soon be struck down again, some 2-10 years later, but may cause damage to society in the meantime.

If politicians need to be afraid of the constitutional court for passing a specific bill, they should not pass it. There is also usually a way to demand an opinion from the court before a bill is passed, which might absolve them in this regard.

Surely the incentives should be set up to avoid unconstitutional laws from ever being passed in the first place, and not to only be active for "short" periods at a time?