SIMD level must be easily controllable at runtime

[ankith26]

moving my comment from #2897 to an issue:

Everytime someone has to test a lower SIMD level they have to mess with either the buildconfig or the source code itself, and this is not ideal. Especially if we want a user to test out something.

One approach is to have env variables PG_ENABLE_[AVX2|SSE2|NEON] that can be configured before pygame init. On init, these variables are read, and along with runtime detection, we set the corresponding runtime check values.

Another approach is to have some API, probably in pygame.system, to pythonically get/set this

A point by @Starbuck5

We will get this for free when SDL3 comes out, btw. SDL_HINT_CPU_FEATURE_MASK.

[itzpr3d4t0r]

This sounds pretty useful, sign me up!

[oddbookworm]

Everytime someone has to test a lower SIMD level they have to mess with either the buildconfig or the source code itself, and this is not ideal. Especially if we want a user to test out something.
One approach is to have env variables PG_ENABLE_[AVX2|SSE2|NEON] that can be configured before pygame init. On init, these variables are read, and along with runtime detection, we set the corresponding runtime check values.

I'm thinking it should actually be kinda the other way around, the env variables disable specific things. We don't want end users to usually have to worry about enabling instruction sets unless they're doing something specific