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_entry/processor.rb

@@ -0,0 +1,95 @@
+class PlaidEntry::Processor
+  # plaid_transaction is the raw hash fetched from Plaid API and converted to JSONB
+  def initialize(plaid_transaction, plaid_account:, category_matcher:)
+    @plaid_transaction = plaid_transaction
+    @plaid_account = plaid_account
+    @category_matcher = category_matcher
+  end
+
+  def process
+    PlaidAccount.transaction do
+      entry = account.entries.find_or_initialize_by(plaid_id: plaid_id) do |e|
+        e.entryable = Transaction.new
+      end
+
+      entry.assign_attributes(
+        amount: amount,
+        currency: currency,
+        date: date
+      )
+
+      entry.enrich_attribute(
+        :name,
+        name,
+        source: "plaid"
+      )
+
+      if detailed_category
+        matched_category = category_matcher.match(detailed_category)
+
+        if matched_category
+          entry.transaction.enrich_attribute(
+            :category_id,
+            matched_category.id,
+            source: "plaid"
+          )
+        end
+      end
+
+      if merchant
+        entry.transaction.enrich_attribute(
+          :merchant_id,
+          merchant.id,
+          source: "plaid"
+        )
+      end
+    end
+  end
+
+  private
+    attr_reader :plaid_transaction, :plaid_account, :category_matcher
+
+    def account
+      plaid_account.account
+    end
+
+    def plaid_id
+      plaid_transaction["transaction_id"]
+    end
+
+    def name
+      plaid_transaction["merchant_name"] || plaid_transaction["original_description"]
+    end
+
+    def amount
+      plaid_transaction["amount"]
+    end
+
+    def currency
+      plaid_transaction["iso_currency_code"]
+    end
+
+    def date
+      plaid_transaction["date"]
+    end
+
+    def detailed_category
+      plaid_transaction.dig("personal_finance_category", "detailed")
+    end
+
+    def merchant
+      merchant_id = plaid_transaction["merchant_entity_id"]
+      merchant_name = plaid_transaction["merchant_name"]
+
+      return nil unless merchant_id.present? && merchant_name.present?
+
+      ProviderMerchant.find_or_create_by!(
+        source: "plaid",
+        name: merchant_name,
+      ) do |m|
+        m.provider_merchant_id = merchant_id
+        m.website_url = plaid_transaction["website"]
+        m.logo_url = plaid_transaction["logo_url"]
+      end
+    end
+end