Account::Sync model and test fixture simplifications (#968)

* Add sync model

* Fresh fixtures for sync tests

* Sync tests overhaul

* Fix entry tests

* Complete remaining model test updates

* Update system tests

* Update demo data task

* Add system tests back to PR checks

* More simplifications, add empty family to fixtures for easier testing

app/models/account/sync.rb

@@ -0,0 +1,51 @@
+class Account::Sync < ApplicationRecord
+  belongs_to :account
+
+  enum :status, { pending: "pending", syncing: "syncing", completed: "completed", failed: "failed" }
+
+  class << self
+    def for(account, start_date: nil)
+      create! account: account, start_date: start_date
+    end
+
+    def latest
+      order(created_at: :desc).first
+    end
+  end
+
+  def run
+    start!
+
+    sync_balances
+
+    complete!
+  rescue StandardError => error
+    fail! error
+  end
+
+  private
+
+    def sync_balances
+      syncer = Account::Balance::Syncer.new(account, start_date: start_date)
+
+      syncer.run
+
+      append_warnings(syncer.warnings)
+    end
+
+    def append_warnings(new_warnings)
+      update! warnings: warnings + new_warnings
+    end
+
+    def start!
+      update! status: "syncing", last_ran_at: Time.now
+    end
+
+    def complete!
+      update! status: "completed"
+    end
+
+    def fail!(error)
+      update! status: "failed", error: error.message
+    end
+end