How to use rowspan to group table cells

[jnachtigall]

I saw that there's Column grouping which does something similar to colspan for Headers at least.

But how could I implement rowspan, that is group row cells? Like the third row in this example with the 2 in it:

Would I have to override some component? If so, which. Sorry I am new to mantine-table (thanks for creating it :-) )

I would also only like to rowspan on the first row probably. Like this, where you have a first row with year with spans over 3 rows / cells: