The HDU filter which corresponds to a given HDU handler.
HduCategory::forClass<Hdu>() -> HduCategory::Any
HduCategory::forClass<Header>() -> HduCategory::Any
HduCategory::forClass<ImageHdu>() -> HduCategory::Image
HduCategory::forClass<ImageRaster>() -> HduCategory::Image
HduCategory::forClass<BintableHdu>() -> HduCategory::Bintable
HduCategory::forClass<BintableColumn>() -> HduCategory::Bintable