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

.cursor/rules/project-conventions.mdc

@@ -71,7 +71,7 @@ Due to the open-source nature of this project, we have chosen Minitest + Fixture
 
 - Always use Minitest and fixtures for testing.
 - Keep fixtures to a minimum.  Most models should have 2-3 fixtures maximum that represent the "base cases" for that model.  "Edge cases" should be created on the fly, within the context of the test which it is needed.
-- For tests that require a large number of fixture records to be created, use Rails helpers such as [entries_test_helper.rb](mdc:test/support/account/entries_test_helper.rb) to act as a "factory" for creating these.  For a great example of this, check out [forward_calculator_test.rb](mdc:test/models/account/balance/forward_calculator_test.rb)
+- For tests that require a large number of fixture records to be created, use Rails helpers such as [entries_test_helper.rb](mdc:test/support/entries_test_helper.rb) to act as a "factory" for creating these.  For a great example of this, check out [forward_calculator_test.rb](mdc:test/models/account/balance/forward_calculator_test.rb)
 - Take a minimal approach to testing—only test the absolutely critical code paths that will significantly increase developer confidence
 
 #### Convention 5a: Write minimal, effective tests
@@ -87,26 +87,26 @@ Below are examples of necessary vs. unnecessary tests:
 # GOOD!!
 # Necessary test - in this case, we're testing critical domain business logic
 test "syncs balances" do
-  Account::Holding::Syncer.any_instance.expects(:sync_holdings).returns([]).once
+  Holding::Syncer.any_instance.expects(:sync_holdings).returns([]).once
 
   @account.expects(:start_date).returns(2.days.ago.to_date)
 
-  Account::Balance::ForwardCalculator.any_instance.expects(:calculate).returns(
+  Balance::ForwardCalculator.any_instance.expects(:calculate).returns(
     [
-      Account::Balance.new(date: 1.day.ago.to_date, balance: 1000, cash_balance: 1000, currency: "USD"),
-      Account::Balance.new(date: Date.current, balance: 1000, cash_balance: 1000, currency: "USD")
+      Balance.new(date: 1.day.ago.to_date, balance: 1000, cash_balance: 1000, currency: "USD"),
+      Balance.new(date: Date.current, balance: 1000, cash_balance: 1000, currency: "USD")
     ]
   )
 
   assert_difference "@account.balances.count", 2 do
-    Account::Balance::Syncer.new(@account, strategy: :forward).sync_balances
+    Balance::Syncer.new(@account, strategy: :forward).sync_balances
   end
 end
 
 # BAD!!
 # Unnecessary test - in this case, this is simply testing ActiveRecord's functionality
 test "saves balance" do 
-  balance_record = Account::Balance.new(balance: 100, currency: "USD")
+  balance_record = Balance.new(balance: 100, currency: "USD")
 
   assert balance_record.save
 end