Start and end balance anchors for historical account balances (#2455)

* Add kind field to valuation

* Fix schema conflict

* Add kind to valuation

* Scaffold opening balance manager

* Opening balance manager implementation

* Update account import to use opening balance manager + tests

* Update account to use opening balance manager

* Fix test assertions, usage of current balance manager

* Lint fixes

* Add Opening Balance manager, add tests to forward calculator

* Add credit card to "all cash" designation

* Simplify valuation model

* Add current balance manager with tests

* Add current balance logic to reverse calculator and plaid sync

* Tweaks to initial calc logic

* Ledger testing helper, tweak assertions for reverse calculator

* Update test assertions

* Extract balance transformer, simplify calculators

* Algo simplifications

* Final tweaks to calculators

* Cleanup

* Fix error, propagate sync errors up to parent

* Update migration script, valuation naming

app/models/account/anchorable.rb

@@ -0,0 +1,52 @@
+# All accounts are "anchored" with start/end valuation records, with transactions,
+# trades, and reconciliations between them.
+module Account::Anchorable
+  extend ActiveSupport::Concern
+
+  included do
+    include Monetizable
+
+    monetize :opening_balance
+  end
+
+  def set_opening_anchor_balance(**opts)
+    opening_balance_manager.set_opening_balance(**opts)
+  end
+
+  def opening_anchor_date
+    opening_balance_manager.opening_date
+  end
+
+  def opening_anchor_balance
+    opening_balance_manager.opening_balance
+  end
+
+  def has_opening_anchor?
+    opening_balance_manager.has_opening_anchor?
+  end
+
+  def set_current_anchor_balance(balance)
+    current_balance_manager.set_current_balance(balance)
+  end
+
+  def current_anchor_balance
+    current_balance_manager.current_balance
+  end
+
+  def current_anchor_date
+    current_balance_manager.current_date
+  end
+
+  def has_current_anchor?
+    current_balance_manager.has_current_anchor?
+  end
+
+  private
+    def opening_balance_manager
+      @opening_balance_manager ||= Account::OpeningBalanceManager.new(self)
+    end
+
+    def current_balance_manager
+      @current_balance_manager ||= Account::CurrentBalanceManager.new(self)
+    end
+end