Panic if steam is not running

[PROMETHIA-27]

I'm using aeronet_steam via the new lightyear release, and running into a panic where if steam is not running/reachable when the game starts, aeronet_steam will panic that SteamworksClient is not inserted into the world because I am unable to create and insert it.

Instead of panicking aeronet_steam should fail more gracefully so that games with steam integration don't crash on startup without a helpful error for an end-user.

Here's the full panic error:

Setting breakpad minidump AppID = 1603000
SteamInternal_SetMinidumpSteamID:  Caching Steam ID:  76561198111281656 [API loaded no]

thread 'main' panicked at C:\Users\elect\.cargo\registry\src\index.crates.io-1949cf8c6b5b557f\aeronet_steam-0.14.0\src\session.rs:43:33:
Requested resource aeronet_steam::SteamworksClient does not exist in the `World`.
                Did you forget to add it using `app.insert_resource` / `app.init_resource`?
                Resources are also implicitly added via `app.add_event`,
                and can be added by plugins.

[aecsocket]

The aeronet_steam plugins currently require Steam to already be initialized, which is admittedly an oversight since you should be able to dynamically choose to use Steam or not at runtime, instead of at plugin build time. Relevant Discord conversation: https://discord.com/channels/691052431525675048/1354455157596880906/1390226707180556308

I think the best approach to fix this is to lazily check for SteamworksClient when you try to use a Steam IO layer for the first time, instead of doing the setup work in the AeronetSteamSessionPlugin.