Load books on first open

[Mqrius]

What

Fixes #845

Bug Details

Initial book loading is gated by ClientAdvancements::onClientPacket to prevent "excessive toast spam", as explained by the comment on that method.

However, when no advancements are registered or no advancements are achieved yet by the player, this never loads the books.

Fix Details

If the books are unloaded at the moment of the player opening the book, then reload the books first.

We do still want to load the books when the first advancements package arrives, because we need to check if we need to toast, so both paths still exist and use a shared source of truth.

[Minecraftschurli]

This PR just moves a boolean flag to another class and adds a single reload point? I'll have a look if this needs to be this difficult.

[Mqrius]

Yeah, though be careful not to try loading them too early in the boot process before things have been sent from the server. I had that issue for a bit until I moved it to load on first book open instead.