Add Binance support, heavily inspired by the Coinbase one (#1317)

* feat: add Binance support (Items, Accounts, Importers, Processor, and Sync)

* refactor: deduplicate 'stablecoins' constant and push stale_rate filter to SQL

---------

Signed-off-by: Juan José Mata <juanjo.mata@gmail.com>
Co-authored-by: Juan José Mata <juanjo.mata@gmail.com>

app/models/binance_account/holdings_processor.rb

@@ -0,0 +1,112 @@
+# frozen_string_literal: true
+
+# Creates/updates Holdings for each asset in the combined BinanceAccount.
+# One Holding per (symbol, source) pair.
+class BinanceAccount::HoldingsProcessor
+  include BinanceAccount::UsdConverter
+
+  def initialize(binance_account)
+    @binance_account = binance_account
+  end
+
+  def process
+    unless account&.accountable_type == "Crypto"
+      Rails.logger.info "BinanceAccount::HoldingsProcessor - skipping: not a Crypto account"
+      return
+    end
+
+    assets = raw_assets
+    if assets.empty?
+      Rails.logger.info "BinanceAccount::HoldingsProcessor - no assets in payload"
+      return
+    end
+
+    assets.each { |asset| process_asset(asset) }
+  rescue StandardError => e
+    Rails.logger.error "BinanceAccount::HoldingsProcessor - error: #{e.message}"
+    nil
+  end
+
+  private
+
+    attr_reader :binance_account
+
+    def target_currency
+      binance_account.binance_item.family.currency
+    end
+
+    def account
+      binance_account.current_account
+    end
+
+    def raw_assets
+      binance_account.raw_payload&.dig("assets") || []
+    end
+
+    def process_asset(asset)
+      symbol = asset["symbol"] || asset[:symbol]
+      return if symbol.blank?
+
+      total  = (asset["total"] || asset[:total]).to_d
+      source = asset["source"] || asset[:source]
+
+      return if total.zero?
+
+      ticker   = symbol.include?(":") ? symbol : "CRYPTO:#{symbol}"
+      security = resolve_security(ticker, symbol)
+      return unless security
+
+      price_usd = fetch_price(symbol)
+      return if price_usd.nil?
+
+      amount_usd = total * price_usd
+
+      # Stale rate metadata is intentionally discarded here — it is captured and
+      # surfaced at the account level by BinanceAccount::Processor#process_account!.
+      amount, _stale, _rate_date = convert_from_usd(amount_usd, date: Date.current)
+
+      # Also convert per-unit price to target currency
+      price, _, _ = convert_from_usd(price_usd, date: Date.current)
+
+      import_adapter.import_holding(
+        security:               security,
+        quantity:               total,
+        amount:                 amount,
+        currency:               target_currency,
+        date:                   Date.current,
+        price:                  price,
+        cost_basis:             nil,
+        external_id:            "binance_#{symbol}_#{source}_#{Date.current}",
+        account_provider_id:    binance_account.account_provider&.id,
+        source:                 "binance",
+        delete_future_holdings: false
+      )
+
+      Rails.logger.info "BinanceAccount::HoldingsProcessor - imported #{total} #{symbol} (#{source}) @ #{price_usd} USD → #{amount} #{target_currency}"
+    rescue StandardError => e
+      Rails.logger.error "BinanceAccount::HoldingsProcessor - failed asset #{asset}: #{e.message}"
+    end
+
+    def import_adapter
+      @import_adapter ||= Account::ProviderImportAdapter.new(account)
+    end
+
+    def resolve_security(ticker, symbol)
+      BinanceAccount::SecurityResolver.resolve(ticker, symbol)
+    end
+
+    def fetch_price(symbol)
+      return 1.0 if BinanceAccount::STABLECOINS.include?(symbol)
+
+      provider = binance_account.binance_item&.binance_provider
+      return nil unless provider
+
+      %w[USDT BUSD FDUSD].each do |quote|
+        price_str = provider.get_spot_price("#{symbol}#{quote}")
+        return price_str.to_d if price_str.present?
+      end
+
+      Rails.logger.warn "BinanceAccount::HoldingsProcessor - no price found for #{symbol} across all quote pairs; skipping holding"
+      nil
+    end
+end