Ensures cross-DB compatibility for all types of both custom and user
profile fields, specifically when they're filtered and/or aggregated.
Implement stress testing of both via appropriate report sources.
Ensure column and filters provided by each source have sufficient
coverage. Re-factor individual entity/helper class tests to test
their own specific implementation only.
Remove now-defunct test fixtures.
We should respect the value of the PHPUNIT_LONGTEST constant in the
report source stress tests, as it was discovered after 165e26fa that
the default configuration of some CIs (GHA) was not sufficient to run
them.
Hence, use the PHPUNIT_LONGTEST to determine whether to execute said
tests. Note this constant is enabled on internal CI.
Implement stress tester methods for iterating over report columns,
aggregation and conditions. Assert that each works correctly in
isolation, and when used in conjunction with other columns.
