Use portable-atomic on platforms without u64 atomics

[linkmauve]

This has been tested on powerpc-unknown-linux-gnu, which supports atomics only up to u32. Without this commit, building kira would fail with:

error[E0432]: unresolved import `std::sync::atomic::AtomicU64`
 --> crates/kira/src/backend/cpal/desktop/stream_manager.rs:6:24
  |
6 |         atomic::{AtomicBool, AtomicU64, Ordering},
  |                              ^^^^^^^^^
  |                              |
  |                              no `AtomicU64` in `sync::atomic`
  |                              help: a similar name exists in the module: `AtomicU32`

Edit: This also depends on not-fl3/quad-rand#23 in order to make the whole testsuite pass, but can be merged independently.

[linkmauve]

I just rebased that PR on top of latest main, nothing much was changed but there was a merge conflict.