Optimise row height props

[billouboq]

Hi, thank you for this library it does work wonderfully well ! 🙏

Was thinking about that :

Is your feature request related to a problem? Please describe.
Not a problem but more of a possible optimisation

Describe the solution you'd like
In Virtualiser we can optimise by passing the row height. This work well for basic table where height is always the same. For more complex one, do you think it can optimise it if we could pass a function with row and index and tell the actual height ?

[inokawa]

Yes. Virtua do synchronous update when measured size is different from the value of itemSize prop (or median of measured sizes if undefined), that will costs sometimes.

Actually, you can pass the item sizes using cache prop, without the suggested fix. Its type is masked in published package, but you can use it with as any for now if necessary.

virtua/src/core/types.ts

Line 7 in 4918f3d

export type InternalCacheSnapshot = [sizes: number[], defaultSize: number];

And I'm considering making the type public because it also seems to be useful for supporting SSR in virtualized masonry component (#788).