Performance optimizations about gdext HOT 4 OPEN

Caching the method bind, builtin method, and utility function pointers with a static OnceLock produces the following speedups:

from gdext.

Manually writing an implementation of StringName::length where i cache: __method_name only, __call_fn only, and both, then running each function 1 million times with black_box in release mode, i get:

from gdext.

caching StringNames in function calls can have a significant improvement. running these functions 1 million times (in a std::hint::black_box(..) call):

fn generate_string_name() {
    let foo = StringName::from("foo");
}

fn cached_string_name() {
    static CACHED: OnceLock<StringName> = OnceLock::new();
    let foo = CACHED.get_or_init(|| StringName::from("foo"));
}

takes on average 0.15 seconds for the first one and 0.0003 seconds for the second one in release mode.

we do make calls like StringName::from("name") a lot in our bindings like for method calls and such.

this does require implementing Send and Sync for StringName, but i think that should be safe. StringName is immutable and i believe thread-safe.

from gdext.

The cached function pointers have been implemented, and with them, StringNames also no longer need to be instantiated on each call.

For anyone interested in deeper insights, I wrote about it here:
https://godot-rust.github.io/dev/ffi-optimizations-benchmarking

from gdext.