Mercury integration (#723)

* Initial mercury impl

* FIX both mercury and generator class

* Finish mercury integration and provider generator

* Fix schema

* Fix linter and tags

* Update routes.rb

* Avoid schema drift

---------

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

test/models/provider/mercury_test.rb

@@ -0,0 +1,29 @@
+require "test_helper"
+
+class Provider::MercuryTest < ActiveSupport::TestCase
+  def setup
+    @provider = Provider::Mercury.new("test_token", base_url: "https://api-sandbox.mercury.com/api/v1")
+  end
+
+  test "initializes with token and default base_url" do
+    provider = Provider::Mercury.new("my_token")
+    assert_equal "my_token", provider.token
+    assert_equal "https://api.mercury.com/api/v1", provider.base_url
+  end
+
+  test "initializes with custom base_url" do
+    assert_equal "test_token", @provider.token
+    assert_equal "https://api-sandbox.mercury.com/api/v1", @provider.base_url
+  end
+
+  test "MercuryError includes error_type" do
+    error = Provider::Mercury::MercuryError.new("Test error", :unauthorized)
+    assert_equal "Test error", error.message
+    assert_equal :unauthorized, error.error_type
+  end
+
+  test "MercuryError defaults error_type to unknown" do
+    error = Provider::Mercury::MercuryError.new("Test error")
+    assert_equal :unknown, error.error_type
+  end
+end