Need sourcegen for accumulator / nextupdate fields

[metalgearsloth]

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So we have stuff like drains or whatever that all start at "update now". This means they all remain in sync throughout the round and if they're doing 1 second updates these are all at the same time.

Ideally they'd all have randomised starts so they don't all tick at the same time. Easiest way would be sourcegen attribute for it.