Refactor sparkline error handling and improve series pre-loading

- Added pre-loading of series in AccountableSparklinesController and AccountsController to catch errors before rendering.
- Updated the accounts view to use the pre-loaded sparkline series variable.
- Adjusted the test for graceful handling of errors in the sparkline series method.

This enhances the robustness of the sparkline feature and improves error visibility in the UI.

app/controllers/accountable_sparklines_controller.rb

@@ -2,6 +2,7 @@ class AccountableSparklinesController < ApplicationController
   def show
     @accountable = Accountable.from_type(params[:accountable_type]&.classify)
 
+    # Pre-load the series to catch any errors before rendering
     @series = Rails.cache.fetch(cache_key) do
       account_ids = family.accounts.active.where(accountable_type: @accountable.name).pluck(:id)
 

app/controllers/accounts_controller.rb

@@ -23,6 +23,8 @@ class AccountsController < ApplicationController
   end
 
   def sparkline
+    # Pre-load the sparkline series to catch any errors before rendering
+    @sparkline_series = @account.sparkline_series
     render layout: false
   rescue => e
     Rails.logger.error "Sparkline error for account #{@account.id}: #{e.message}"