OperatorsRegistry & middleware contracts

[mempirate]

Context

Even with this off-chain registry, we'll still have to deploy an OperatorsRegistry eventually for integration with restaking protocols, which require on-chain entrypoints for restaking & operator registration etc. The choice to do this now comes from:

1. The fact that we'll need it eventually
2. We have most of these contracts already, just need to adapt it
3. It would actually allow us to integrate with real collateral and restaking protocols immediately
4. We'd have an on-chain source of truth for the amount of operators & amount of collateral that everyone can monitor

High-level Tasks

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1. Migrate relevant contracts to this repo
2. Simplify and refactor as much as possible
3. Ensure events contain all data required for off-chain sync
4. Drop notions of "active" operator, collateral is optional