Reads an .rds file written with saveRDS() from any NACHO version.
NACHO 2 objects go through upgrade_nacho().
NACHO 3 objects are rebuilt with the current class, because each saved S7
object carries a copy of the class it was made with.
Details
Only read files you trust: readRDS() can run code stored in a crafted
file, notably in R before 4.4.0.