Fix CPU affinity during startup

[FileEX]

Summary

Previously, CPU affinity was set during early process initialization (Core constructor / startup hook). At that point, GTA had not yet finished creating its worker threads, which could result in the affinity mask not being properly respected. This caused inconsistent performance. The affinity logic has now been moved to the Direct3D device creation stage, when the game has completed its main initialization and all major threads have been spawned.

Motivation

Test plan

N/A

Checklist

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