Fix regressions + ignore unknown participants + cache experiments

[smathot]

This PR mainly fixes two issues related to the client.

• Regressions introduced in Multi devices #39 (which I missed during initial testing)
• omm_announce: ignore unknown participants #32
• Experiment resource files are not cached #38 and Temp pool ressouce files written on disk on each trial #24 (which are the same issue)

@gdesor I'm not assigning this to you for review, but please do check this PR hasn't broken your custom detectors. (It should be fine, but I do not have these devices to properly test myself.)

[gdesor]

I can’t test it at the moment. I only have one board and it’s currently used in production, so it’s difficult for me to run tests right now. However, I should receive new ones in the coming days/weeks, but I’ll need to set up the whole setup beforehand.

[smathot]

@gdesor No urgent need to test from our side. But do keep on the radar that you should check this before using it in production.