fix: SocketRegistry-related fixes

[nadir-akhtar]

Motivation:

Various references and uses of the SocketRegistry contract are either incomplete or inconsistent with existing practices.

Changes

• In the SlashingRegistryCoordinator, fixes a bug where the SocketRegistry was not being added to the total list of registries
• Improves the SocketRegistry inheritance pattern to align with existing inheritance patterns (base contract -> abstract storage contract -> interface)
• Adds a missing external function to the interface ISlashingRegistryCoordinator for exposing the SocketRegistry immutable, to be consistent with all other registries
• Removes the unused modifier onlyCoordinationOwner from the SocketRegistry and related contracts / tests
• Updates documentation across contracts to accurately reflect the inclusion of the SocketRegistry into the codebase
• Updates licenses from MIT -> BUSL-1.1, as is consistent with the codebase
• Fixes a misset gap in SocketRegistryStorage from 48 to 49, as there is only one state variable

Impact

• Code correctness improvement
• Accuracy of docs
• Consistency with other sections of the codebase