Update to .NET 8 (new)

[Wartori54]

Second part of #791. This PR builds off of #827.
Remarks:

• Ideally the NLua submodule should be updated to .NET 8 as well before merging this, but its not strictly required.
• This change is known to cause issues in regards to code mod building (mods will have to change their TargetFramework entry to net8.0 in order to build with this version of everest), already built mods aren't affected though.
• MacOS support for low 10.x. versions is unknown currently but the game has been ran on a vm and successfully booted.
• TASes have been tested against this version and are known to sync.
• Added a new log statement in order to facilitate the diagnosis of issues related to the runtime version upgrade.

[maddie480]

are there any blockers for this?

[Wartori54]

The 2nd and 3rd point, which we can't really do much about, we just have accept them, although i could make a updating guide wiki article to send to people that complain about why their mod doesn't build anymore. But saving MacOS sounds kinda hard, everest core already left out some even older versions of MacOS, so i guess its not too bad either, its not our fault apple doesn't provide new updates to their moderately old devices.