message: refactor: remove redundant handling for overwriting rules
diff: -import { isCallable, merge } from '@vee-validate/shared';
  +import { isCallable } from '@vee-validate/shared';
  import { ValidationRuleFunction } from './types';
  const RULES: Record<string, ValidationRuleFunction> = {};
  export class RuleContainer {
  public static extend(name: string, validator: ValidationRuleFunction) {
  - // if rule already exists, overwrite it.
  - if (RULES[name]) {
  - RULES[name] = merge(RULES[name], validator);
  - return;
  - }
  -
  RULES[name] = validator;
  }
  