Refactor kompilation cache in the intergration tests

[geo2a]

As a follow-up to #2417, @tothtamas28 suggest we should do the following:

As I see it, tests basically require an interface that takes a Target and returns a Path to the kompiled target (in the actual tests there might be another indirection from spec files to targets, but I'll not consider this for simplicity).

So you just have to ensure that Target -> Path is reproducible between runs, then accommodating both use cases (prekompiled vs on-the-fly) is straightforward.

If the Path does not exist, lock and kompile
Otherwise, return the Path.

For prekompiled mode, you pass in a non-empty directory as base. For on-the-file mode, you pass in an empty temporary directory.

cache, etc. can be dropped, the actual cache is the file system.