Centralize CI config and make it more uniform (Adds macOS arm64 pypy CI)

[ankith26]

The goal of this PR is to centralize all common cibuildwheel config, and make our CI more uniform.

We currently take different strategies on different workflows. manylinux takes the "build for all pythons in one workflow per arch" strategy. Mac takes an (ever so slightly harder to maintain) strategy of handwritten "split jobs evenly" while windows takes the "every run on its own" thing. I figured that the strategy manylinux takes is actually the most efficient, even if it's slower than the rest. Why?

• We can re-use more stuff across runs - cibuildwheel dependencies, buildtime dependencies, SDL prebuilt downloads (in windows) and doc building.
• By using less concurrent workflows per PR we are actually making room for more across-PR CI concurrency.
• Simpler config to maintain. Want to support a new python version on CI? It's now a one line change in pyproject.toml
• There is no real advantage from a PR maker POV if all windows builds can finish in 8 minutes, and the linux one is going to take like 15 minutes anyways which the PR maker has to wait for.
• It is also wasteful if there is say, a windows specific CI fail that just causes multiple separate runs to fail when one fail would be enough to convey the message.

Also switches build backend to build[uv] which should again save some CI time.

I may also explore more in the caching area in future PRs and see how that improves things.

[ankith26]

While doing this PR I also happened to

• Add CI for pypy arm64 on macOS which we completely missed somehow
• Add numpy-based tests on linux

Here is a table of cumulated-time comparisons, along with per config notes

Platform	Before (main)	After (this PR)	Extra Notes
Windows x86_64	37m 33s (3m 37s, 3m 10s, 3m 52s, 4m 23s, 4m 13s, 4m 30s, 4m 50s, 8m 58s)	15m 19s	Numpy tests removed on pypy 3.10
Windows x86	19m 22s (4m 16s, 3m 5s, 4m 6s, 4m 45s, 3m 10s)	9m 10s	-
macOS arm64	15m 0s (10m 23s, 4m 37s)	10m 15s	Added 3 new pypy runs
macOS x86_64	27m 7s (7m 49s, 8m 30s, 10m 48s)	15m 8s	Numpy tests removed on pypy 3.10
Linux arm64	13m 43s	11m 48s	Added numpy for tests where possible
Linux x86_64	11m 43s	10m 44s	Added numpy for tests where possible
Linux x86	12m 58s	11m 1s	-