Remove Dask from stochastic noise plugin

[maxwhitemet]

Addresses #1131

Description
This PR removes the use of Dask from the stochastic noise plugin, and adds two processing options:

• supply a cube with a realization dimension to iterate over serially.
• extract (before using this plugin) each realization into its own cube, run each through the plugin with a scheduler, and merge (after using this plugin) the cubes together.

Testing:

• Ran tests and they passed OK
• Added new tests for the new feature(s)

[gavinevans]

Thanks @maxwhitemet 👍

I've added one comment.

[maxwhitemet]

Thanks @gavinevans. I have implemented the suggested changes