Choose Antags Before Job Selection

[formlessnameless]

Essentially makes it so all antag gamerules choose which player will be an antag before job selection runs. It gets all added gamerules, including pending ones, and then selects based on the player pool at the start of the round. There's still a LOT to test with this and I will probably make a bunch of changes as I revisit things but this seems to be a Technically Working Prototype. I wanted to get this draft up so other code knowledge havers could take a look and tell me if there's things I'm being stupid about. I know at the very least I want to add a bit that double checks the counts and adds more antags when each rule actually starts if the ratios are off.

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• tweak: Antagonist selection now happens before job selection.