Balance sheet cache layer, non-blocking sync UI (#2356)

* Balance sheet cache layer with cache-busting

* Update family cache timestamps during Sync

* Less blocking sync loaders

* Consolidate family data caching key logic

* Fix turbo stream broadcasts

* Remove dev delay

* Add back account group sorting

app/models/balance_sheet/sync_status_monitor.rb

@@ -0,0 +1,35 @@
+class BalanceSheet::SyncStatusMonitor
+  def initialize(family)
+    @family = family
+  end
+
+  def syncing?
+    syncing_account_ids.any?
+  end
+
+  def account_syncing?(account)
+    syncing_account_ids.include?(account.id)
+  end
+
+  private
+    attr_reader :family
+
+    def syncing_account_ids
+      Rails.cache.fetch(cache_key) do
+        Sync.visible
+            .where(syncable_type: "Account", syncable_id: family.accounts.active.pluck(:id))
+            .pluck(:syncable_id)
+            .to_set
+      end
+    end
+
+    # We re-fetch the set of syncing IDs any time a sync that belongs to the family is started or completed.
+    # This ensures we're always fetching the latest sync statuses without re-querying on every page load in idle times (no syncs happening).
+    def cache_key
+      [
+        "balance_sheet_sync_status",
+        family.id,
+        family.latest_sync_activity_at
+      ].join("_")
+    end
+end