Reduce test sizes

[swfsql]

The tests already are reasonably small and are fast to run eg. even on the CPU. But when simulating the execution through miri, various tests take more than half an hour, with one in transformers taking one hour. So one possibility to make this easier is to reduce the test sizes to their minimum, as long as they reach their testing goal.

Another benefit for a miri pass when reducing the tests is their memory requirements, as this tends to increase the longer the test needs to run, reaching 2GB of ram per test on the longest ones. So reducing their memory peak should make it easier to run more tests in parallel.

There are 367 tests, with many taking 10~20 seconds. So just focusing on what takes more than a few minutes could already be sufficient for the purpose of running all tests.

[swfsql]

Closing as I think the tests that got run on the linked pr indicated a robust behavior.
But feel free to ping or re-open in case anyone has an interest!