This PR:
- Sets up the slasher infrastructure with the base functionality
required (in `ISlasher.sol`, `SlasherBase.sol` and
`SlasherBaseStorage.sol`) and adds the tests for it (in
`SlasherBase.t.sol`).
- Adds an implementation of a more complex slasher (in
`IVetoableSlasher.sol` and `VetoableSlasher.sol`) and tests for it (in
`VetoableSlasher.t.sol`).
- Modifies the `ServiceManagerBase` contract to use the new
`VetoableSlasher` contract to manage slashing.
- Updates mocks and tests to reflect the newly added functionality.
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Co-authored-by: Facundo Farall <37149322+ffarall@users.noreply.github.com>
