Fix manga details for non-library manga taking longer to load

[FlaminSarge]

Fixes #3027
Regression from #2955 (probably)

Moves setDefaultChapterFlags after the initial load so at least the Manga details page shows up while fetches are still happening. Also avoids setting default chapter flags if default is the same as the manga's current flags (for no defaults set or if this is reopening a non-favorite).

The problem seemed to be that the mangas DB write from setMangaDefaultChapterFlags had to wait for a long time (150+ms on my emulator with a 6000+ library). Not sure if that's due to the mutex changes for DB transactions or something else, but on top of that it also increased the time that availableScanlators and excludedScanlators took; also unsure why that is.

Before these changes, timing was something like this:

  D  MangaScreen [<title>] awaitManga: 0ms
  D  MangaScreen [<title>] awaitChapters: 1ms
  D  MangaScreen [<title>] setDefaultFlags: 179ms
  D  MangaScreen [<title>] availableScanlators: 296ms
  D  MangaScreen [<title>] excludedScanlators: 379ms
  D  MangaScreen [<title>] State.Success: 381ms

After the changes:

  D  MangaScreen [<title>] awaitManga: 0ms
  D  MangaScreen [<title>] awaitChapters: 1ms
  D  MangaScreen [<title>] availableScanlators: 2ms
  D  MangaScreen [<title>] excludedScanlators: 2ms
  D  MangaScreen [<title>] State.Success: 2ms
  D  MangaScreen [<title>] setDefaultFlags: 422ms

And if setting the default flags gets to no-op because the default chapter flags are 0 or the same as before, that takes barely any time as well.

availableScanlators/excludedScanlators await's don't have to be moved out of the state update block, but I figured it doesn't hurt and can prevent pain later if those also need to be debugged again (moved them around to get timings for those initially, left them there afterwards).

[FlaminSarge]

Note that this should still probably go in despite #2982 being a good rework of the root cause, since currently any time a non-favorite is opened it triggers a mangas db write when it doesn't need to.