Increase test coverage to 95%+

[maifeeulasad]

Willing to work on this one, along with community

[chen-jiying]

Putting up a PR for this. src/ coverage 36% → 97% (105 tests).
Added vitest.config.ts to scope coverage to src/ (examples/ was pulling it to 8%) and tests for utils + browser/index methods.
browser.ts 25% → 100%
utils.ts 49% → 94%
index.ts 0% → 97%
@maifeeulasad anything from Jan? Don't want to overlap.
cc @BruceMacD @jmorganca