mre: chrome may not gc FileReader output inside WebWorkers

select a file around 16 MiB large: 

screenshot after selecting Windows.UI.Xaml.dll (17'110 KiB)
which should have consumed 16 * 16 = ~256 MiB RAM at most

this bug occurs when repeatedly reading a file using FileReaders
in WebWorkers; this mre version (unlike v1) has each WebWorker
create its own FileReader, which is then reused for all reads

older versions of chrome had a similar bug triggered by creating
a new FileReader for each read operation, not necessary this time

observed on:
* macos 15.1.1 + chr 131.0.6778.140 (latest gchrome arm64 stable)
* win10 1809 (17763.6532) + chr 132.0.6834.32 (latest gchrome beta)
* win10 1809 (17763.6532) + chr 133.0.6876.4 (latest gchrome dev)
* android 15 + chromium 133.0.6891.0

NOT observed on:
* win10 1809 (17763.6532) + chr 131.0.6778.140 (latest gchrome stable)
* macos 14.2.1 + chr 131.0.6778.86 (NOT-latest gchrome arm64 Stable)
* android 15 + vanadium 131.0.6778.104
* archlinux + chromium 131.0.6778.108
* fedora + chromium 131.0.6778.85
* macos + firefox
* win10 + firefox