feat: add browser based tests

[SgtPooki]

we should ensure we're testing that browser use of the library works as expected in a proper browser environment.

We're currently using vitest, so we can add browser tests with https://vitest.dev/guide/browser/#configuration. I know synapse-sdk uses playwright-test to run mocha tests in a browser environment, so maybe we want to do that, but that would be a lot of test re-writing.

related: #172 (comment)

[rvagg]

@SgtPooki fwiw I'm agnostic about testing frameworks, I started using vitest here simply because it was the new hotness and I wanted to try it out. But it's likely too immature to support all of what we want so maybe just going to Mocha would be best. I'd be fine with switching to a similar testing stack as Synapse, and it probably wouldn't be very hard to switch.

[BigLep]

2025-10-30 conversation:

• We want to change to Mocha and do playwright tests like Synapse (without pnpm)
• We're not putting this in M3.5 because we're going to rely on "catching it in production", where our production is "filecoin-pin-website".