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>

test/models/binance_account/holdings_processor_test.rb

@@ -0,0 +1,72 @@
+# frozen_string_literal: true
+
+require "test_helper"
+
+class BinanceAccount::HoldingsProcessorTest < ActiveSupport::TestCase
+  setup do
+    @family = families(:dylan_family)
+    @family.update!(currency: "EUR")
+
+    @item = BinanceItem.create!(
+      family: @family, name: "Binance", api_key: "k", api_secret: "s"
+    )
+    @ba = @item.binance_accounts.create!(
+      name: "Binance",
+      account_type: "combined",
+      currency: "USD",
+      current_balance: 1000,
+      raw_payload: {
+        "assets" => [ { "symbol" => "BTC", "total" => "0.5", "source" => "spot" } ]
+      }
+    )
+    @account = Account.create!(
+      family: @family,
+      name: "Binance",
+      balance: 0,
+      currency: "EUR",
+      accountable: Crypto.create!(subtype: "exchange")
+    )
+    AccountProvider.create!(account: @account, provider: @ba)
+  end
+
+  test "converts holding amount to family currency when exact rate exists" do
+    ExchangeRate.create!(from_currency: "USD", to_currency: "EUR",
+                         date: Date.current, rate: 0.92)
+
+    Security.find_or_create_by!(ticker: "CRYPTO:BTC") do |s|
+      s.name = "BTC"
+      s.exchange_operating_mic = "XBNC"
+    end
+
+    BinanceAccount::HoldingsProcessor.any_instance
+      .stubs(:fetch_price).with("BTC").returns(60_000.0)
+
+    import_adapter = mock
+    import_adapter.expects(:import_holding).with(
+      has_entries(currency: "EUR", amount: 27_600.0)
+    )
+    Account::ProviderImportAdapter.stubs(:new).returns(import_adapter)
+
+    BinanceAccount::HoldingsProcessor.new(@ba).process
+  end
+
+  test "uses raw USD amount when no rate is available" do
+    ExchangeRate.stubs(:find_or_fetch_rate).returns(nil)
+
+    Security.find_or_create_by!(ticker: "CRYPTO:BTC") do |s|
+      s.name = "BTC"
+      s.exchange_operating_mic = "XBNC"
+    end
+
+    BinanceAccount::HoldingsProcessor.any_instance
+      .stubs(:fetch_price).with("BTC").returns(60_000.0)
+
+    import_adapter = mock
+    import_adapter.expects(:import_holding).with(
+      has_entries(currency: "EUR", amount: 30_000.0)
+    )
+    Account::ProviderImportAdapter.stubs(:new).returns(import_adapter)
+
+    BinanceAccount::HoldingsProcessor.new(@ba).process
+  end
+end