Refactor tests and benchmarks

[Nerixyz]

Description

This PR makes a few changes:

• Tests and benchmarks run on the main thread

  • This caused network tests to fail, since they rely on the Qt event-loop. These were adjusted to use qWaitFor which keeps the event-loop spinning. Since this is actually declared in QtCore, no dependency to the Test component is necessary.

• Running benchmarks/tests related to emojis would segfault (at least for me with MSVC), because the ImageExpirationPool would be destroyed before the Image from getEmpty (the destructor calls removeImagePtr).

  The fix for this is a bit more involved, as it's not trivial to control the order of destruction of static inside functions, so the statics are moved inside an anonymous namespace.
  Creating a ImageExpirationPool when starting up will cause the freeTimer_ to not work, as the main thread isn't running yet. That's why it's created lazily.

  For the emoji tests/benchmarks, this will cause QObject::startTimer: Timers can only be used with threads started with QThread to be printed after they're finished, because that's the first time the ImageExpirationPool is accessed (when destroying the empty image). This can be fixed by e.g. calling ImageExpirationPool::instance() somewhere before/during the tests/benchmarks, but it's not really an issue here, since we're about to destroy the pool regardless (thus the timer would've never fired).

• The tests for filters failed on Qt 6 (filters are probably not fully working in Qt 6, so this could be a separate PR).

• https://httpbin.org was really slow for me at times, and sometimes it even timed out. I found https://postman-echo.com, which has the same API except for the special 402 status response.

Now the following is possible:

• Running all tests in debug mode (this means that assertions will fire!).
• Using ctest.

[github-actions]

clang-tidy made some suggestions

[Nerixyz]

and use ctest

It doesn't actually use ctest - but it could: ctest -j$(nproc) --output-on-failure (optionally with -T test).

[github-actions]

clang-tidy made some suggestions