See #12769 for the motivation. We set the 4MB not only for the main
thread, but also for all tokio and rayon threads to fix a stack overflow
while unpacking wheels in production on Windows.
There are two variables for setting the stack size: A new
`UV_STACK_SIZE` that takes precedent, and the existing `RUST_MIN_STACK`.
When setting the stack size, `UV_STACK_SIZE` should be preferred, since
`RUST_MIN_STACK` affects all Rust applications, including build backends
we call (e.g., maturin). The minimum stack size is set to 1MB, the
lowest stack size we observed on a platform (Windows main thread).
Fixes#12769
## Test Plan
Tested manually with the example from #12769
Christopher Tee
Charlie Marsh
konsti