Altair test-vectors at fork transition

[potuz]

There are a few edge case situations that may happen at the Altair fork and are currently under-tested:

• A validator is slashed in phase0 and is active but slashing at the fork and thus leaking. It may or not be a member of a sync committee, we need to check the right penalties.
• A validator started an exit in phase0 and is put in a queue, check these queues, either active or leaking at the fork.
• Quadratic leaking in case of network not finalizing at the fork.
• An activator deposited in phase0 and is in the queue at the fork.

Many of these tests are done already at Altair, but implementations may differ in the way they compute rewards/penalties if a slashing event for example happened before the fork. Thus this could eventually lead to a consensus failure with the cost of only slashing a single validator.

This is follow up from discussions in
https://discord.com/channels/595666850260713488/598292067260825641/897248922706255893