[Status Network Contracts] Account can prevent slashing by creating many vaults

[0x-r4bbit]

Context: https://github.com/Cyfrin/audit-2025-12-statusl2/issues/11

While it has been a known risk that users can create too many vaults and therefore DDOS themselves,
we haven't considered that this also enables them to prevent slashing.

This needs fixing.
The only way to fix this is to introduce a limit on vaults that can be created.

We've discussed this in the past and faced some complexities related to migrating vaults.
Time to revisit this.