Expectations re-order and corrected FA3 skip

[remi-or]

This PR changes the order of priority of Expectations to prefer the default expectation over the cross-device match as discussed with @ydshieh . It also changes the decorator of a FA3 test from require_flash_attn to require_flash_attn_3

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[ydshieh]

Thanks.

If it is not clear from any where, maybe add a comment about what a default will look like.

I am using (None, None). And a comment like

A default value is usually a value that is used for some time in a test before it uses Expectations. When we modify a test to use Expectations for a specific hardware, we don't want to affect the tests on other hardware. So we add a value for that specific hardware and leave the previously existing value as the default value which will be used by the other hardwares. This is why the default value is preferred over using the values from other hardwares.

might help, if you find so.

[ydshieh]

Feel free to merge 🤗

[remi-or]

Good ideas! Did both. Will merge after tests pass.