Partial revert of #17405, implement LAG_INIT

[Sovexe]

About the PR

• Partial revert of Adds some sweet optimisations, plus some minor ones. #17405
• Reverts the sleep(-1) calls back to LAGCHECK calls
• Implements new less aggressive LAG_INIT used by these procs to salvage some of the performance lost
• Implements LAGCHECK_IF_LIVE(x) to allow local servers to keep using sleep(-1)

Why's this needed?

• Attempting to reduce round start judder

[Laboredih123]

alas, if only there was a way to both go fast and to let people in quickly simultaneously. also not sure if 95 will be sufficient for local testing on weaker computers