Plaid sync domain improvements (#2267)

Breaks our Plaid sync process out into more manageable classes. Notably, this moves the sync process to a distinct, 2-step flow:

1. Import stage - we first make API calls and import Plaid data to "mirror" tables
2. Processing stage - read the raw data, apply business rules, build internal domain models and sync balances

This provides several benefits:

- Plaid syncs can now be "replayed" without fetching API data again
- Mirror tables provide better audit and debugging capabilities
- Eliminates the "all or nothing" sync behavior that is currently in place, which is brittle

app/models/plaid_item/importer.rb

@@ -0,0 +1,53 @@
+class PlaidItem::Importer
+  def initialize(plaid_item, plaid_provider:)
+    @plaid_item = plaid_item
+    @plaid_provider = plaid_provider
+  end
+
+  def import
+    fetch_and_import_item_data
+    fetch_and_import_accounts_data
+  rescue Plaid::ApiError => e
+    handle_plaid_error(e)
+  end
+
+  private
+    attr_reader :plaid_item, :plaid_provider
+
+    # All errors that should halt the import should be re-raised after handling
+    # These errors will propagate up to the Sync record and mark it as failed.
+    def handle_plaid_error(error)
+      error_body = JSON.parse(error.response_body)
+
+      case error_body["error_code"]
+      when "ITEM_LOGIN_REQUIRED"
+        plaid_item.update!(status: :requires_update)
+        raise error
+      else
+        raise error
+      end
+    end
+
+    def fetch_and_import_item_data
+      item_data = plaid_provider.get_item(plaid_item.access_token).item
+      institution_data = plaid_provider.get_institution(item_data.institution_id).institution
+
+      plaid_item.upsert_plaid_snapshot!(item_data)
+      plaid_item.upsert_plaid_institution_snapshot!(institution_data)
+    end
+
+    def fetch_and_import_accounts_data
+      snapshot = PlaidItem::AccountsSnapshot.new(plaid_item, plaid_provider: plaid_provider)
+
+      snapshot.accounts.each do |raw_account|
+        plaid_account = plaid_item.plaid_accounts.find_or_initialize_by(
+          plaid_id: raw_account.account_id
+        )
+
+        PlaidAccount::Importer.new(
+          plaid_account,
+          account_snapshot: snapshot.get_account_data(raw_account.account_id)
+        ).import
+      end
+    end
+end