remove makeNotifierFromAsyncIterable from vat-timer

[turadg]

What is the Problem Being Solved?

It's a "hot notifier" in the updater is driving the changes instead of the client. In a cold notifier the client asks for the next update and the notifier figures out what to do. Is doesn't any activity at all until the client calls next() again.

Description of the Design

Most of the uses of makeNotifierFromAsyncIterable take subscriptions so they'll be converted in #5695 to use the new function for those cases.

These two don't:

agoric-sdk/packages/SwingSet/src/vats/timer/vat-timer.js

Lines 66 to 73 in cafa284

	const iterable = makeTimedIterable(
	timerService.delay,
	timerService.getCurrentTimestamp,
	baseTime,
	interval,
	);
	const notifier = makeNotifierFromAsyncIterable(iterable);

agoric-sdk/packages/zoe/tools/fakePriceAuthority.js

Lines 233 to 256 in cafa284

	async function* generateQuotes(amountIn, brandOut) {
	let record = await ticker.getUpdateSince();
	while (record.updateCount) {
	// eslint-disable-next-line no-await-in-loop
	const { value: timestamp } = record; // = await E(timer).getCurrentTimestamp();
	yield priceInQuote(amountIn, brandOut, timestamp);
	// eslint-disable-next-line no-await-in-loop
	record = await ticker.getUpdateSince(record.updateCount);
	}
	}
	/** @type {PriceAuthority} */
	const priceAuthority = Far('fake price authority', {
	getQuoteIssuer: (brandIn, brandOut) => {
	assertBrands(brandIn, brandOut);
	return quoteIssuer;
	},
	getTimerService: (brandIn, brandOut) => {
	assertBrands(brandIn, brandOut);
	return timer;
	},
	makeQuoteNotifier: async (amountIn, brandOut) => {
	assertBrands(amountIn.brand, brandOut);
	return makeNotifierFromAsyncIterable(generateQuotes(amountIn, brandOut));

@michaelfig suspects the latter may solve a leak so tagging this with 'performance'.

Security Considerations

--

Test Plan

--

[warner]

#5763 now tracks the zoe portion, this ticket now only tracks the swingset portion.

[warner]

I'll handle this as part of the #5668 rewrite of vat-timer/device-timer

[warner]

The new vat-timer implements the Notifier API directly, without using makeNotifierFromAsyncIterable. It implements the Iterable API directly too. The memory usage should be proportional to the number of unresolved Promises fetched by clients with getUpdateSince() and next(), respectively.