Fix flaky tests and refactor ObjectService

[lanedirt]

This PR contains the following:

• Fixes flaky tests by ensuring all feature tests start with the same static time (2024-01-01). Some tests for building queues and fleet missions rely on advancing the time and testing whether missions have been processed and planets have been updated. Having all tests start with the same time ensures there are no conflicts. Addresses [BUG] Fix flaky espionage dispatch mission test #401.
• Refactor ObjectService to be a static class instead of dependency injected as it contains no dependencies. This simplifies the code by not having to inject ObjectService into many places but instead be able to call it like ObjectService::getObjectXXX() instead.
• Make SettingsService a proper singleton so any changes made to the settings are available everywhere preventing cache issues.

[lanedirt]

I'm waiting with merging this until other open PR's are merged, as this refactor can cause conflicts with existing work in progress.