Change initializeSapling to avoid cloning

The Sapling parameters defined in `ironfish::sapling_bls12::SAPLING` are
behind a `lazy_static`. As such, the parameters are not loaded until
accessed fo the first time. The purpose of `initializeSapling` is to
acccess the parameters to ensure that they get loaded early.

The current implementation of `initializeSapling` was calling `.clone()`
on `ironfish::sapling_bls12::SAPLING`, causing large amounts of memory
to be allocated and written, only to be discarded shortly afterwards.
The implementation has been changed to just dereference `SAPLING`,
without doing anything else. This is enough to trigger `lazy_static` to
load the parameters.

Also:

- Removed the `Arc` from `ironfish::sapling_bls12::SAPLING`: `Arc` is
  used to extend lifetimes in multithreaded environments, but the
  lifetime of `SAPLING` is static, so there's no point in extending it.

- Removed `ironfish::sapling_bls12::load` because it's not public and
  redundant

ironfish-rust-nodejs/src/lib.rs

@@ -122,7 +122,8 @@ pub fn generate_key_from_private_key(private_key: String) -> Result<Key> {
 
 #[napi]
 pub fn initialize_sapling() {
-    let _ = sapling_bls12::SAPLING.clone();
+    // Deref the `SAPLING` lazy-static, to ensure it gets initialized
+    let _ = &*sapling_bls12::SAPLING;
 }
 
 #[napi(constructor)]

ironfish-rust/src/sapling_bls12.rs

@@ -1,24 +1,14 @@
 /* This Source Code Form is subject to the terms of the Mozilla Public
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
-pub use blstrs::Scalar;
-use lazy_static::lazy_static;
-use std::sync::Arc;
 
 use crate::Sapling;
+use lazy_static::lazy_static;
+
+pub use blstrs::Scalar;
 
 // Loads the Sapling object once when dereferenced,
 // then reuses the reference on future calls.
 lazy_static! {
-    pub static ref SAPLING: Arc<Sapling> = Arc::new(load());
-}
-
-/// Load a sapling object configured to a BLS12 jubjub curve. This is currently
-/// the only pairing for which a jubjub curve has been defined, and is the
-/// default implementation.
-///
-/// Provided as a convenience method so clients don't have to depend
-/// explicitly on zcash_primitives just to define a JubjubBls12 point.
-fn load() -> Sapling {
-    Sapling::load()
+    pub static ref SAPLING: Sapling = Sapling::load();
 }