Add fixes related to the openzeppelin audit

[FedokDL]

L-01 Lack of Input Validation
the _layerZeroEndpoint and _minter addresses are never validated.

1. _layerZeroEndpoint validates on deploy on @layerzerolabs/lz-evm-oapp-v2/contracts/oapp/OAppCore.sol:30
2. Added validation for _minter.

L-02 Incorrect Docstring
Fixed

N-01 Missing Docstring
Documentation is done in the interface to the smart contract. We will not make changes here.

N-02 Lack of Security Contact.
No change.

Other:

• @layerzero contracts updated to the latest version from https://github.com/LayerZero-Labs/LayerZero-v2/commits/main/. Commit hash: 1fde89479fdc68b1a54cda7f19efa84483fcacc4;
• fix codestyle;
• remove virtual from the 'burn' functions;