Account:: namespace simplifications and cleanup (#2110)

* Flatten Holding model

* Flatten balance model

* Entries domain renames

* Fix valuations reference

* Fix trades stream

* Fix brakeman warnings

* Fix tests

* Replace existing entryable type references in DB

app/models/holding/gapfillable.rb

@@ -0,0 +1,38 @@
+module Holding::Gapfillable
+  extend ActiveSupport::Concern
+
+  class_methods do
+    def gapfill(holdings)
+      filled_holdings = []
+
+      holdings.group_by { |h| h.security_id }.each do |security_id, security_holdings|
+        next if security_holdings.empty?
+
+        sorted = security_holdings.sort_by(&:date)
+        previous_holding = sorted.first
+
+        sorted.first.date.upto(Date.current) do |date|
+          holding = security_holdings.find { |h| h.date == date }
+
+          if holding
+            filled_holdings << holding
+            previous_holding = holding
+          else
+            # Create a new holding based on the previous day's data
+            filled_holdings << Holding.new(
+              account: previous_holding.account,
+              security: previous_holding.security,
+              date: date,
+              qty: previous_holding.qty,
+              price: previous_holding.price,
+              currency: previous_holding.currency,
+              amount: previous_holding.amount
+            )
+          end
+        end
+      end
+
+      filled_holdings
+    end
+  end
+end