`bsa::fo4::File::write_directx` uses the wrong `arraySize` for cubemaps

[Ryan-rsm-McKenzie]

According to the docs, texture arrays for cubemaps are supposed to be a multiple of 6 in length. We currently write 1 unconditionally as the length. Hopefully someone who actually understands dds files can chime in to help use understand how to compute the correct number.

bsa/src/bsa/fo4.cpp

Line 745 in 2e16e3a

.arraySize = 1,

[Guekka]

From DirectXTex wiki:

arraySize should be 1 for non-array resources. For cubemaps it should be 6. For cubemap arrays it should be a multiple of 6 (i.e. numCubes = arraySize / 6).

I don't think I've ever encountered a cubemap array, so we can probably ignore this case (?)

We know if the texture is a cubemap from the flags

So I'd say we can use .arraySize = (this->header.flags & 1u) != 0 ? 6 : 1

Maybe we should introduce a helper function isCubemap

[Guekka]

It looks like you already do that in the Rust library https://github.com/Ryan-rsm-McKenzie/bsa-rs/blob/7b90ce145d5de8e1dda280f10b2b0e0b5aa067f9/src/fo4/file.rs#L1386C1-L1386C56