feat: adding freezer role

[ihoroleksiienko]

Main changes

1. The new freezer role has been added to the contract. That role must be assigned to accounts that are executed the frozen balance related functions, like: freezeIncrease(), freezeDecrease(), transferFrozen().
2. A new function named configureFreezerBatch() has been created to configure the freezer role for a batch of accounts.
3. A new modifier named onlyFreezer has been added to substitute onlyBlockclister modifier and checks if caller is freezer for the related functions.

Function declaration

  /**
   * @notice Configures a batch of freezers
   *
   * Emits a {FreezerAssigned} event for each assigned freezer
   *
   * Emits a {FreezerRemoved} event for each removed freezer
   *
   * @param freezers The array of freezer addresses to configure
   * @param status The new status of the freezers: `true` is to assign freezers, `false` is to remove freezers
   */
  function configureFreezerBatch(address[] calldata freezers, bool status) external;

Function details

Emitted events

The new function triggers new events FreezerAssigned and FreezerRemoved:

    /**
     * @notice Emitted when a freezer account is assigned
     *
     * @param freezer The address of the assigned freezer
     */
    event FreezerAssigned(address indexed freezer);

    /**
     * @notice Emitted when a freezer account is removed
     *
     * @param freezer The address of the removed freezer
     */
    event FreezerRemoved(address indexed freezer);

Reverting Conditions

The new function is reverted (failed) if:

1. The contract is paused, with error message "Pausable: paused" .
2. The caller is not owner, with error message Ownable: caller is not the owner.
3. The freezer status is the same as previously set for one of the provided accounts, with AlreadyConfigured error.

Test coverage

New functionality was fully covered with tests