Chainlink VRF v2.5 plus OpenZeppelin fails to compile: duplicate OwnershipTransferred event (5883) and fulfillRandomWords memory/calldata mismatch (7723)

Symptom: adding Chainlink VRF v2.5 (VRFConsumerBaseV2Plus) to a contract that already inherits OpenZeppelin Ownable breaks forge build with two errors that look unrelated:

Error (5883): Event with same name and parameter types defined twice.
  --> lib/chainlink/.../ConfirmedOwnerWithProposal.sol:13
  Note: Other declaration is here: lib/openzeppelin-contracts/contracts/access/Ownable.sol:33
Error (7723): Data locations of parameters have to be the same when overriding
  non-external functions, but they differ.  --> src/...:fulfillRandomWords

Cause 1: VRFConsumerBaseV2Plus already inherits Chainlink's ConfirmedOwner, which declares its own event OwnershipTransferred(address,address). Inheriting OpenZeppelin Ownable as well puts two identical event signatures in one contract, which Solidity rejects. VRF v2.5 changed this — the older VRFConsumerBaseV2 had no ownership built in, so codebases migrating from v2 suddenly get the clash.

Fix 1: drop Ownable from the inheritance list and use the ownership functions VRF already gives you (owner(), onlyOwner, transferOwnership) — or keep Ownable and inherit the coordinator interface directly instead of VRFConsumerBaseV2Plus. Do not try to override the event; events are not overridable.

Cause 2: in v2.5 the callback signature changed to uint256[] calldata randomWords (v2 used memory), and Solidity requires an override to match the data location exactly for non-external functions.

Fix 2:

function fulfillRandomWords(uint256 requestId, uint256[] calldata randomWords) internal override { ... }

Also note v2.5 widened subscriptionId from uint64 to uint256, so constructor and request plumbing must be updated in the same pass.

Source: adapted from a Stack Exchange answer by SYED ASAD KAZMI (question by Giuliano Maria Lodi), https://ethereum.stackexchange.com/questions/164508/migration-to-vrf-2-5-resolving-conflicts-between-chainlink-vrf-v2-5-and-openze — CC BY-SA 4.0