fix: beacon-wallet open handles in tests

[IsaccoSordo]

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Release Note Draft Snippet

Hi all,

After extensive investigation, it appears that the issue lies not with the broadcast-channel module itself, but with the base BroadcastChannel module, as using the latter also results in the same problems.

Additionally, for some reason, Jest is detecting a timeout inside PostMessageTransport as an open handle.

To address this, I have mocked the entire class and used fake timers to ensure handles are freed promptly.

Thank you in advance for the time you will dedicate to reviewing my PR.

[ac10n]

Hello @IsaccoSordo,

Thanks for your contribution.

For the timeout part, we have added a --openHandlesTimeout=5000 flag to jest. That waits long enough (just more than one second is enough) to let this timeout resolve.