Adds FFI function to release a handle

src/ffi/ffi_handle.rs

@@ -9,6 +9,20 @@ use std::hash::Hash;
 use std::sync::atomic::AtomicUsize;
 use std::sync::{Arc, LazyLock};
 
+/// This function can be called from the FFI to release a handle when it is no longer needed. This
+/// does not drop the object per se, but will reduce the reference count of the object. If the object
+/// is then no longer referenced, it will be dropped.
+#[no_mangle]
+extern "C" fn ffi_release_handle(handle: usize) {
+    let mut write_lock = FFI_OBJECTS.write();
+    let mut write_lock_inverse = FFI_OBJECTS_INVERSE.write();
+
+    let obj = write_lock.remove(&handle);
+    if let Some(obj) = obj {
+        write_lock_inverse.remove(&obj);
+    }
+}
+
 /// A handle of an object that can be passed over FFI. We use this to avoid passing pointers over the
 /// FFI boundary. This allows us to be able to move the data around in memory without having to worry
 /// about the pointers being invalidated. It also allows us to have a type-safe interface.