Expose Once within std-shims, bump spin to 0.9

This is technically a semver break due to bumping spin to 0.10, with the types
from spin being directly exposed. Long-term, we should not directly expose spin
but instead have our own types which are thin wrappers around spin (clearly
defining our API and allowing upgrading internals without breaking semver).

Cargo.lock

@@ -9613,6 +9613,12 @@ version = "0.9.8"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "6980e8d7511241f8acf4aebddbb1ff938df5eebe98691418c4468d0b72a96a67"
 
+[[package]]
+name = "spin"
+version = "0.10.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d5fe4ccb98d9c292d56fec89a5e07da7fc4cf0dc11e156b41793132775d3e591"
+
 [[package]]
 name = "spki"
 version = "0.7.3"
@@ -9689,7 +9695,7 @@ name = "std-shims"
 version = "0.1.2"
 dependencies = [
  "hashbrown 0.14.5",
- "spin 0.9.8",
+ "spin 0.10.0",
 ]
 
 [[package]]

common/std-shims/Cargo.toml

@@ -17,7 +17,7 @@ rustdoc-args = ["--cfg", "docsrs"]
 workspace = true
 
 [dependencies]
-spin = { version = "0.9", default-features = false, features = ["use_ticket_mutex", "lazy"] }
+spin = { version = "0.10", default-features = false, features = ["use_ticket_mutex", "once", "lazy"] }
 hashbrown = { version = "0.14", default-features = false, features = ["ahash", "inline-more"] }
 
 [features]

common/std-shims/README.md

@@ -3,4 +3,9 @@
 A crate which passes through to std when the default `std` feature is enabled,
 yet provides a series of shims when it isn't.
 
-`HashSet` and `HashMap` are provided via `hashbrown`.
+No guarantee of one-to-one parity is provided. The shims provided aim to be sufficient for the
+average case.
+
+`HashSet` and `HashMap` are provided via `hashbrown`. Synchronization primitives are provided via
+`spin` (avoiding a requirement on `critical-section`).
+types are not guaranteed to be

common/std-shims/src/sync.rs

@@ -26,6 +26,6 @@ mod mutex_shim {
 pub use mutex_shim::{ShimMutex as Mutex, MutexGuard};
 
 #[cfg(feature = "std")]
-pub use std::sync::LazyLock;
+pub use std::sync::{OnceLock, LazyLock};
 #[cfg(not(feature = "std"))]
-pub use spin::Lazy as LazyLock;
+pub use spin::{Once as OnceLock, Lazy as LazyLock};