cvm-rs: Switch thread pool to rayon

Much less underhanded than using an IO library's capability to do so. Also, rayon will make encoding multiple jpegs in parallel *much* easier.

tbh if i do that I may also switch to napi-rs, it seems a bit less painful and supports much more async shenigans.

(Also, it will actually bind classes properly... something Neon really sucks at unless you look at strange documentation.)

cvm-rs/Cargo.toml

@@ -14,5 +14,5 @@ libc = "0.2.155"
 
 # Required for JPEG
 once_cell = "1.19.0"
-tokio = { version = "1.38.0", features = [ "rt", "rt-multi-thread" ] }
 turbojpeg-sys = "1.0.0"
+rayon = "1.10.0"