* feat(slot-reservations): Allow slots to be reserved
Closes#175.
Allows reservation of slots, without an implementation of the expanding window.
- Add a function called `reserveSlot(address, SlotId)`, that allows three unique addresses per slot to be reserved, that returns bool if successful.
- Use `mapping(SlotId => EnumerableSet.AddressSet)`
- Return false if the address could not be added to the set (if `EnumerableSet.add` returns false)
- Add `canReserveSlot(address, SlotId)`
- Return `true` if set of reservations is less than 3 and the set doesn't already contain the address
- Return `true` otherwise (for now, later add in logic for checking the address is inside the expanding window)
- Call `canReserveSlot` from `reserveSlot` as a `require` or invariant
- Add `SlotReservations` configuration struct to the network-level config, with `maxReservations`
