Add support for pytorch-lightning 2.0.0

[cweniger]

Currently Swyft crashes with PL 2.0.0. Swyft should be updated without breaking backward compatibility with PL 1.9.0 and earlier.

[cweniger]

Even after the above merge there are issues when running "infer" with lightning 2.0.0, because of some incomplete limitations of the CombinedLoader in 2.0.0. This probably will solve itself over time as 2.x.x becomes more stable. For now the recommendation will be to stick to 1.9.x.

[cweniger]

Recent discussions in pl here:

• Support all iterator modes for fit/validate/test/predict Lightning-AI/pytorch-lightning#16830
• Support all CombinedLoader modes during evaluation Lightning-AI/pytorch-lightning#17163

But it still looks like it will not solve all problems (predict loop is not touched).

[cweniger]

Solution strategy: Write custom CombinedLoader within swyft. Might also be useful for #133