Optimize the WASI random_get implementation. (#4917)

* Optimize the WASI `random_get` implementation.

Use `StdRng` instead of the `OsRng` in the default implementation of
`random_get`. This uses a userspace CSPRNG, making `random_get` 3x faster
in simple benchmarks.

* Update cargo-vet audits for cap-std 0.25.3.

* Update all cap-std packages to 0.25.3.

crates/wasi-common/cap-std-sync/src/lib.rs

@@ -141,5 +141,5 @@ impl WasiCtxBuilder {
 }
 
 pub fn random_ctx() -> Box<dyn RngCore + Send + Sync> {
-    Box::new(cap_rand::rngs::OsRng::default(ambient_authority()))
+    Box::new(cap_rand::std_rng_from_entropy(cap_rand::ambient_authority()))
 }