Add an option for fast tests by gating slow tests to extended_tests feature #19228

Is your feature request related to a problem or challenge?

It would be great to have a testing option that achieves good coverage while remaining fast to run (on the order of tens of seconds). When working on complex changes, after each small atomic step I want to run a quick test suite to gain confidence that things are still correct, but running the full test suite is currently too slow.

On my MacBook Pro (M4 Pro), cargo nextest run takes around 2 minutes 30 seconds.

I believe most tests are very fast, and only a small number are slow (e.g., fuzz tests). We could move these slow tests under an extended_tests feature.

There are already existing tests gated by this feature:

Once slow tests are moved, the fast test suite can be run with:

cargo nextest run

Ideally, this completes within one minute.

To run the full test suite, use:

cargo nextest run --features ...,extended_tests,...

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