Fix SyncOrAsync util syncValue transfer

Our `SyncOrAsync` util is used for cases where a task is >99% of the time
synchronous, yet <1% of the time asynchronous, and where we don't want to
incur any overhead/supplementary complexity of awaiting a Promise which
inherently schedule a microtask when the value is most probably already
there.

It worked well for most usages, but it turns out that a task that starts
as asynchronous would then always lead to the need to rely on Promises,
even once the task is finished (basically, if it started as an "async
value" it could never transform itself to a "sync value").

This does not create any issue but we could gain some minuscule advantage
(well, we could argue that `SyncOrAsync`'s advantage is in itself
minuscule) here by just relying on the value synchronously once the task is
finished.

src/utils/sync_or_async.ts

@@ -78,12 +78,14 @@ const SyncOrAsync = {
    * @returns {Object}
    */
   createAsync<T>(val: Promise<T>): ISyncOrAsyncValue<T> {
-    let ret = null;
-    val.then((resolved) => {
+    let ret: T | null = null;
+    val.then((resolved: T) => {
       ret = resolved;
     }, noop);
     return {
-      syncValue: ret,
+      get syncValue(): T | null {
+        return ret;
+      },
       getValueAsAsync() {
         return val;
       },