Add synced `Spring.IsPaused`

Pause state seems to be synced, but its getter is tied to `Spring.GetGameSpeed`, which is unsynced because of gamespeed. The request is to add `Spring.IsPaused() -> bool` which would be synced. Perhaps gamespeed could also be made synced, in which case there wouldn't need to be a split, but that is not in the scope of this request.

Start by tracing the existing Spring.GetGameSpeed getter and the pause-state handling it relies on. Add the requested synced Spring.IsPaused() -> bool entry point without expanding the scope to syncing gamespeed; done means callers can obtain pause state through the new synced API.

Written by the indexing model from the issue text.