Support for 32-bit architectures?

[jszwedko]

It looks like currently this crate doesn't build on powerpc-unknown-linux-gnu:

➜  metrics git:(main) cargo build --target=powerpc-unknown-linux-gnu
   Compiling serde v1.0.130
   Compiling prost v0.7.0
   Compiling tracing v0.1.29
   Compiling thiserror v1.0.30
   Compiling metrics v0.17.0 (/home/jesse/workspace/metrics/metrics)
error[E0432]: unresolved import `std::sync::atomic::AtomicU64`
 --> metrics/src/key.rs:7:32
  |
7 |     sync::atomic::{AtomicBool, AtomicU64, Ordering},
  |                                ^^^^^^^^^
  |                                |
  |                                no `AtomicU64` in `sync::atomic`
  |                                help: a similar name exists in the module: `AtomicU8`

error: aborting due to previous error

We discovered this by way of a user trying to compile vector for powerpc-unknown-linux-gnu.

Is this a platform this crate would be interested in supporting? I imagine this would mean generally supporting 32-bit architectures.

[tobz]

No issue with trying to support them, nope!

Likely just need to do something like this across the entire crate.