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

.dialyzer_ignore.exs

@@ -0,0 +1,5 @@
+[
+  # Mix task warnings - these are false positives due to dialyzer limitations with Mix tasks
+  {"lib/mix/tasks/generate_fixtures.ex", :callback_info_missing},
+  {"lib/mix/tasks/generate_fixtures.ex", :unknown_function}
+]