WIP(meteor3): boot progresses past linker + several async fixes

Past the client-bundle underscore linker (pin underscore@1.6.4) and now working
through the server async/await migration on Meteor 3.1 + Mongo 7:

- Removed fibers (imports/startup/server/fibers.js + import) — gone in Meteor 3.
- accounts/oauth.js: upsert -> upsertAsync (top-level await).
- migrations.js: startup async + await Migrations.migrateTo (async in 2.x).
  mongo7 marked at version 18 so historical up() bodies (still sync Mongo) don't
  run — prod data restores already-migrated. Documented.
- subsUnion.js: fully async (fetchAsync/findOneAsync/countAsync/upsertAsync,
  observeAsync with async callbacks).
- facts.js: dropped dead sync findOne.
- email.js: ostrio:mailer 2.5 is a default export (was named import); dropped
  removed static MailTime.Template (built-in default '{{{html}}}').

NEXT wall + remaining chain (multi-session):
1. aldeed:collection2@4.2.0 needs simpl-schema 3.x (app has 1.x) -> 'attachSchema
   is not a function'. Requires upgrading npm simpl-schema to 3.x and migrating
   all collection schemas (SimpleSchema.RegEx.Id etc.) across ~8 files.
2. Rest.js + helpers (countRealFires/firesUnion/whichAreFalsePositives/
   fireFromHash/subscriptionsInsert/upsertFalsePositive) -> *Async.
3. Patch vendored restivus to await async endpoint handlers.
4. methods/publications/comments to async; cron SyncedCron(quave)/Facts imports.
5. alanning:roles@1.2.10 + gadicohen:sitemaps@0.0.17 warn incompatible -> bump.
6. React 16 -> 18 render root.

Run with: NODE_OPTIONS='--dns-result-order=ipv4first --no-network-family-autoselection'
MONGO_URL='mongodb://localhost:27019/fuegos?replicaSet=rs0'

imports/startup/server/subsUnion.js

@@ -11,7 +11,7 @@ import { isMailServerMaster } from '/imports/startup/server/email';
 
 // sudo apt-get install libcairo2-dev libjpeg-dev libgif-dev
 
-Meteor.startup(() => {
+Meteor.startup(async () => {
   if (!isMailServerMaster) {
     console.log('We only process subsUnion in master');
     return;
@@ -35,8 +35,8 @@ Meteor.startup(() => {
 
   const noNoisy = sub => sub;
 
-  const process = (isPublic) => {
-    const subscribers = Subscriptions.find().fetch();
+  const process = async (isPublic) => {
+    const subscribers = await Subscriptions.find().fetchAsync();
     const result = calcUnion(L, subscribers, isPublic ? addNoisy : noNoisy, true);
     const union = result[0];
     const bounds = result[1];
@@ -74,9 +74,9 @@ Meteor.startup(() => {
       };
       // FIXME, take care of object size:
       // https://stackoverflow.com/questions/10827812/what-is-the-length-maximum-for-a-string-data-type-in-mongodb-used-with-ruby
-      SiteSettings.upsert({ name: `subs-${publicl}-union` }, unionSet, { multi: false });
-      SiteSettings.upsert({ name: `subs-${publicl}-union-bounds` }, boundsSet, { multi: false });
-      SiteSettings.upsert({ name: 'subs-union-count' }, sizeSet, { multi: false });
+      await SiteSettings.upsertAsync({ name: `subs-${publicl}-union` }, unionSet, { multi: false });
+      await SiteSettings.upsertAsync({ name: `subs-${publicl}-union-bounds` }, boundsSet, { multi: false });
+      await SiteSettings.upsertAsync({ name: 'subs-union-count' }, sizeSet, { multi: false });
       if (debug) console.log(`${Publicl} subscription union calculated`);
     } else {
       console.log('Subscription union failed!');
@@ -84,40 +84,39 @@ Meteor.startup(() => {
   };
 
   // At startup, we check if it's necessary to calc subscriptions union again
-  const currentUnion = SiteSettings.findOne({ name: 'subs-public-union' });
-  const lastSubs = Subscriptions.findOne({}, { sort: { updatedAt: -1 } });
-  const countUnionSubs = SiteSettings.findOne({ name: 'subs-union-count' });
-  const countSubs = Subscriptions.find({}).count();
+  const currentUnion = await SiteSettings.findOneAsync({ name: 'subs-public-union' });
+  const lastSubs = await Subscriptions.findOneAsync({}, { sort: { updatedAt: -1 } });
+  const countUnionSubs = await SiteSettings.findOneAsync({ name: 'subs-union-count' });
+  const countSubs = await Subscriptions.find({}).countAsync();
   if (currentUnion && lastSubs) {
     const lastUnionUpdated = currentUnion.updatedAt;
     const lastSubsUpdated = lastSubs.updatedAt;
     if (lastUnionUpdated > lastSubsUpdated || !countUnionSubs || countSubs !== countUnionSubs.value) {
       console.log('Subs union outdated');
-      process(true);
-      process(false);
+      await process(true);
+      await process(false);
     } else {
       console.log('Subs union up-to-date');
     }
   }
 
-  Subscriptions.find({ createdAt: { $gt: new Date() } }).observe({
-    added: function newSubAdded() { // doc) {
+  const recreate = async () => { await process(true); await process(false); };
+
+  await Subscriptions.find({ createdAt: { $gt: new Date() } }).observeAsync({
+    added: async function newSubAdded() { // doc) {
       if (debug) console.log('Subs added so recreate union');
-      process(true);
-      process(false);
+      await recreate();
     }
   });
 
-  Subscriptions.find().observe({
-    changed: function subsChanged() { // updatedDoc, oldDoc) {
+  await Subscriptions.find().observeAsync({
+    changed: async function subsChanged() { // updatedDoc, oldDoc) {
       if (debug) console.log('Subs changed so recreate union');
-      process(true);
-      process(false);
+      await recreate();
     },
-    removed: function subsRemoved() { // oldDoc) {
+    removed: async function subsRemoved() { // oldDoc) {
       if (debug) console.log('Subs removed so recreate union');
-      process(true);
-      process(false);
+      await recreate();
     }
   });
 });