feat(contracts): EL middleware

[merklefruit]

This PR introduces the BoltEigenLayerMiddlewareV1 contract, supporting the new ELIP-02 protocol upgrade.

Flow to register as a new EigenLayer Operator in bolt:

1. Register as a new EL operator (only necessary if you aren't an operator already, otherwise can be skipped)
   • delegationManager.registerAsOperator()
2. Register as an operator in the bolt AVS:
   • allocationManager.registerForOperatorSets()
   • arguments need to specify the correct AVS address (the bolt middleware created in this PR) as well as the operator sets that they wish to join. By default these are left up to governance and will dictate which strategies can be used.

Additionally, this PR refactors some internals of the OperatorsRegistry. Mainly:

1. switched to PausableEnumerableSet (library from symbiotic-sdk) to be able to pause/unpause operators.

Setup:

• the eigenlayer-contracts submodule is pointing to the slashing feature branch: slashing-magnitudes
• OZ dependencies are using v5.2.0 (openzeppelin-contracts-upgradeable and openzeppelin-contracts)

Tests:

• Register as an operator through the EL middleware
• Deposit collateral to a strategy and delegate to an operator
• Update AVS operator shares for that strategy
• Read collateral of the operator on the middleware

Meta

• closes part of OperatorsRegistry & middleware contracts #4