CloneRepo compilation significantly slows down loading scripts

The CloneRepo script is currently not compiled at build-time, this is because it has dependencies on internal Bitbucket API classes which must be resolved at runtime via the @WithPlugin annotation

The above isn't so much of an issue, however this specific class takes a significant amount of time to compile, this seems to be due to the Groovy compiler doing excessive classloading for invalid classnames, see Groovy issue: GROOVY-9236

On my machine, the compilation for CloneRepo alone is taking 20+ seconds due to the above bug in the Groovy compiler, this happens every time the app is reinstalled, because this clears our Groovy compiler cache.

We can't immediately move to Groovy 3.x.x, so we must find a way to make the above compilation happen at build-time.