feat: Add vitest suite

[bdougie]

We really should have a vitest suite. The PR #109 adds a getRelativeDays function that can be tested.

import { getRelativeDays } from './dateUtils';

describe('getRelativeDays', () => {
  it('returns "-" for 0 days', () => {
    expect(getRelativeDays(0)).toBe('-');
  });

  it('returns "1d" for 1 day', () => {
    expect(getRelativeDays(1)).toBe('1d');
  });

  it('returns "30d" for 30 days', () => {
    expect(getRelativeDays(30)).toBe('30d');
  });

  it('returns "1mo" for 31 days', () => {
    expect(getRelativeDays(31)).toBe('1mo');
  });

  it('returns "1y" for 365 days', () => {
    expect(getRelativeDays(365)).toBe('1y');
  });

  it('returns "2y" for 730 days', () => {
    expect(getRelativeDays(730)).toBe('2y');
  });
});

Originally posted by @bdougie in #111 (comment)

[Nanak360]

Yup.
PR #111 can be merged once we have the vitest library intigrated in the app. Or, even if it is merged, we can create one more PR for writing test cases.
Also if needed vitest can be added in PR #111 itself with unit tests for the getRelativeDays file