Add Credo configuration and Dialyzer ignore file

- Introduced a new Credo configuration file for code quality checks. - Added a Dialyzer ignore file to suppress known
warnings. - Removed TODO comments for Bulgarian and Icelandic IBANs. - Updated the Dialyzer configuration in mix.exs to
include

.credo.exs

@@ -0,0 +1,22 @@
+%{
+  configs: [
+    %{
+      name: "default",
+      files: %{
+        included: ["lib/", "test/"],
+        excluded: [~r"/_build/", ~r"/deps/", ~r"/node_modules/"]
+      },
+      checks: %{
+        enabled: [
+          {Credo.Check.Design.TagTODO, exit_status: 0},
+          {Credo.Check.Design.TagFIXME, exit_status: 0}
+        ],
+        disabled: [
+          # Validator functions legitimately need higher complexity
+          {Credo.Check.Refactor.CyclomaticComplexity, []},
+          {Credo.Check.Refactor.Nesting, []}
+        ]
+      }
+    }
+  ]
+}