wsclean is the main / only imager currently supported. As it executes it interacts with a set of fits images throughout deconvolution. Depending on their size, number of output channels etc there can be a rather large I/O burden to the disk supporting the filesystem.

Its been found that when many workflows are running concurrently there can be noticeable strain, and sometimes this can causes glitches to the filesystem, slow reads, freezes etc.

This change uses a hold_then_move_into context manager that configures wsclean outputs to be written to some other location, and then moved into place along side the corresponding MS. In practice, on a HPC it is useful to set this to refer to a local disk or a ram disk through appropriate environment variables that are evaluated as the wsclean command is being constructed and executed.