ADD IBAN FIELD TO STRUCTS AND UPDATE PARSING LOGIC

- Added `iban` field to the `IbanEx.Iban` struct to hold the full IBAN value. - Updated the parsing logic to populate
the new field. - Adjusted BBAN rules and tests for France and Brazil to reflect updated structures. - Improved error
handling and format validation routines.

README.md

@@ -15,6 +15,7 @@ In just a few letters and numbers, the IBAN captures all of the country, bank, a
   ```elixir
       iex>  "FI2112345600000785" |> IbanEx.Parser.parse()
       {:ok, %IbanEx.Iban{
+        iban: "FI2112345600000785",
         country_code: "FI",
         check_digits: "21",
         bank_code: "123456",