timers: check for undefined instead of nullish value

[gurgunday]

Now that the Priority Queue heap is a PACKED array, we can safely check if the value is undefined instead of nullish here

Relevant code:

node/lib/internal/priority_queue.js

Lines 11 to 32 in 32851f3

	#heap = [undefined, undefined];
	#setPosition;
	#size = 0;
	constructor(comparator, setPosition) {
	if (comparator !== undefined)
	this.#compare = comparator;
	if (setPosition !== undefined)
	this.#setPosition = setPosition;
	}
	insert(value) {
	const heap = this.#heap;
	const pos = ++this.#size;
	heap[pos] = value;
	this.percolateUp(pos);
	}
	peek() {
	return this.#heap[1];
	}

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 88.52%. Comparing base (32851f3) to head (0c18b90).

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #60124      +/-   ##
==========================================
- Coverage   88.53%   88.52%   -0.02%     
==========================================
  Files         703      703              
  Lines      207833   207833              
  Branches    40014    40011       -3     
==========================================
- Hits       184011   183981      -30     
- Misses      15821    15859      +38     
+ Partials     8001     7993       -8     

Files with missing lines	Coverage Δ
lib/internal/timers.js	99.58% <100.00%> (ø)

... and 28 files with indirect coverage changes

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[aduh95]

But why?

[gurgunday]

The only values in the queue are undefined and TimersList, checking explicitly against undefined communicates this more clearly - I myself thought null could somehow be in the queue when I first read this part

We do the same when shifting the FixedQueue at task_queues, where only null and TickObject are in the list :

node/lib/internal/process/task_queues.js

Line 75 in b757a8f

while ((tock = queue.shift()) !== null) {

I'm trying to align the various queue codes and their usage a little bit, but I can close the PR if you think nullish check is still fine