Net worth calculation (#508)

* Add classification generated column to account

* Add basic net worth calculation

* Add net worth tests

* Fix lint errors

db/migrate/20240302145715_add_classification_to_accounts.rb

@@ -0,0 +1,18 @@
+class AddClassificationToAccounts < ActiveRecord::Migration[7.2]
+  def change
+    change_table :accounts do |t|
+      t.virtual(
+        :classification,
+        type: :string,
+        stored: true,
+        as: <<-SQL
+          CASE
+            WHEN accountable_type IN ('Account::Loan', 'Account::Credit', 'Account::OtherLiability')
+            THEN 'liability'
+            ELSE 'asset'
+          END
+        SQL
+      )
+    end
+  end
+end