proposal: add shorthand rule for throwing mock implementations

[nami8824]

Summary

Vitest 4.1 added mockThrow and mockThrowOnce as shorthand APIs for mocks that throw:

mock.mockThrow(new Error('error message'))
mock.mockThrowOnce(new Error('first call error'))

Currently, eslint-plugin-vitest has shorthand rules for returned values and promises:

• prefer-mock-return-shorthand
• prefer-mock-promise-shorthand

However, throwing mock implementations are still not covered.

This proposes adding a new rule, tentatively named prefer-mock-throw-shorthand, that reports mockImplementation / mockImplementationOnce callbacks whose only behavior is throwing a value.

Examples

Invalid:

vi.fn().mockImplementation(() => {
  throw new Error('error message');
});

mock.mockImplementationOnce(() => {
  throw new Error('error message');
});

Valid:

vi.fn().mockThrow(new Error('error message'));

mock.mockThrowOnce(new Error('error message'));