Make unit tests run in a browser

[peaBerberian]

This mega-PR rewrites unit tests so they can be run in a web browser (for now Chrome + Firefox), through webdriverio - just like our integration and memory tests.

This allows us to run unit tests in the actual environment where the RxPlayer will run and to have a common script + environment for unit, integration and memory tests, thus simplifying the project.

The main difficulty was linked to our over-reliance on vitest's doMock+importActual functions, the second which has a different behavior when run in a web browser: multiple importActual calls in the same test file won't re-evaluate that imported file. This means that doMock performed in-between importActual calls for the same file won't have an impact on that file.

This might be fixed in the future, but I wanted to see how most people succeeded to run vitest in a browser. It seems that relying on a top-level mock function is much more idiomatic, while relying on the hoisted function to also declare hoisted mocks whose implementation can change in-between tests.

Though, to ensure portability between test frameworks if we ever change it (JavaScript is like that sometimes), I try to limit reliance on that vitest-specific vi.mock/vi.hoisted concept, by prefering just mocking through only the more portable spyOn when possible.

[github-actions]

? Automated performance checks have passed on commit 726200f37b5d3d04ac91d72d0d0016bcfca5843d with the base branch dev.

Details

Performance tests 1st run output

No significative change in performance for tests:

Name	Mean	Median
loading	18.94ms -> 19.17ms (-0.231ms, z: 0.80197)	26.10ms -> 26.10ms
seeking	16.94ms -> 14.94ms (2.007ms, z: 0.85447)	10.65ms -> 10.65ms
audio-track-reload	25.47ms -> 25.54ms (-0.075ms, z: 0.32319)	37.20ms -> 37.20ms
cold loading multithread	45.27ms -> 44.55ms (0.726ms, z: 14.07348)	66.90ms -> 65.70ms
seeking multithread	44.94ms -> 39.01ms (5.929ms, z: 0.76597)	9.95ms -> 10.05ms
audio-track-reload multithread	25.10ms -> 25.14ms (-0.037ms, z: 0.82929)	37.05ms -> 36.90ms
hot loading multithread	14.45ms -> 14.32ms (0.129ms, z: 5.42006)	21.15ms -> 21.00ms