DOCS: Additional examples of non-exportable objects

[HenrikBengtsson]

I try to keep track of non-exportable object examples in the Non-Exportable Objects vignette. Let's use this issue to gather additional examples of packages and object classes that cannot be exported to another R process or saved to be used in another R session.

Additional examples:

• Package raster, e.g. raster::writeStart() (https://stackoverflow.com/questions/65148384)
• Package xboost, e.g. xgboost::xgb.DMatrix() (https://stackoverflow.com/questions/65136945/issues-with-running-xgboost-in-multiple-r-processes)
• Package terra, e.g. SpatRaster and SpatVector (https://stackoverflow.com/questions/67445883/terra-package-returns-error-when-try-to-run-parallel-operations). Mention also terra::wrap() for "marshalling"
• Bioconductor package ShortRead, e.g. 'FastqStreamerList' (https://support.bioconductor.org/p/9135851/)