[FEAT] sync subscription utility

[aricart]

[FEAT] added a utility function syncIterator() to wrap an AsyncIterables so that elements can be extracted in a sync faction. Note messages and elements will continue to buffer in the iterable, so if you don't drain it or stop its source memory will grow - this is syntactic sugar, as the iterator can be had via src[Symbol.asyncIterator](). This can be useful to process subscription messages one at a time; this is especially true on tests.

const sub = nc.subscribe("foo");
nc.publish("foo");
nc.publish("foo");
const sync = syncIterator(sub);
console.log((await sync.next()).subject);
console.log((await sync.next()).subject);

[scottf]

LGTM

[Jarema]

LGTM!