Build: Use Github Actions caching instead of SBT caching

[alexklibisz]

Related Issue

• Migrate the build from Gradle to SBT #360

Changes

• Revert the changes made in #360: SBT build caching (pullRemoteCache, pushRemoteCache) #428 . Instead of using SBT's caching mechanisms (pushRemoteCache, pullRemoteCache), use Github Action's caching mechanisms to just cache the target directories. More details below.
• Add @DoNotDiscover on the RecallSuite, as it's mis-behaving again (RecallSuite tests are extremely slow in Github Actions #400). It passes fine locally, so it seems like some sort of throttling or contention in Github actions.

Some more details on caching:

There was a subtle problem with SBT's caching: the succeeded_tests file used by the testQuick command stores the timestamp at which each test suite last succeeded. The next time you run testQuick, if the test suite has been recompiled after that stored timestamp, the test will run-again. I thought that using pullRemoteCache would mean that the tests are not recompiled. That turns out to not be exactly the case. The test is compiled extremely quickly (<= 1s for full compilation), but it's nevertheless re-compiled. That means it needs to be executed, despite having already passed according to the succeeded_tests file.

It turns out that caching each of the target directories solves this problem, and it's probably simpler overall, anyways. The target directory contains the old compilation state and the succeeded_tests file. So if a test suite hasn't changed, it genuinely just won't be recompiled, and so the test suite won't re-run.

The caching action is documented here: Caching dependencies to speedup workflows

Testing and Validation

• Standard CI