Collision While Setting Versions

[dsanders11]

Under certain circumstances, such as opening an example from the docs, multiple versions end up being set in parallel - the original version on startup, immediately followed by the version specified for the example being loaded. Once they're running in parallel, they can collide on setting the active version on disk with fiddle-core.

This situation could be improved by:

• Not unzipping a version until it is run (fix: don't install version until run #1367)
• Keeping track of any in-progress versions being set and the ability to abort them - ideally also aborting the download, but that is not supported by @electron/get at this time. Aborting an in-progress version being set should at least not conflict with any subsequent versions set.