Source tests could reuse analysis data

[euclio]

If the tests haven't changed, we could save some work by not regenerating the analysis data.

[mgattozzi]

Hmmm... cargo runs tests in parallel so it might be a bit harder to cache data, but this would be a good improvement.

[euclio]

I don't think the parallelism would be a problem because the analysis data is per-test.

[mgattozzi]

Ah I misunderstood how it worked. Thanks for clearing that up