Add version compatibility check with Kani

[celinval]

Requested feature: The VSCode extension should warn users if they are using a version of Kani that is incompatible with the extension version.
Use case: The extension exposes fairly unstable features in Kani, and changes to them can make the extension stop working properly without any warning to the user. The same is true if Kani is updated but not the extension. Thus, there should be a compatibility check in the extension that at least warns users of this disparity and recommend either updating Kani or the extension.