Use custom country module to resolve flags more accurately

Ported from https://github.com/wojtekmaj/country-code-to-flag-emoji
(MIT)

test/music_library/country_test.exs

@@ -0,0 +1,46 @@
+defmodule MusicLibrary.CountryTest do
+  use ExUnit.Case, async: true
+
+  alias MusicLibrary.Country
+
+  describe "to_emoji/1" do
+    test "converts alpha-2 codes" do
+      assert Country.to_emoji("US") == "🇺🇸"
+      assert Country.to_emoji("PL") == "🇵🇱"
+      assert Country.to_emoji("GB") == "🇬🇧"
+    end
+
+    test "is case insensitive" do
+      assert Country.to_emoji("us") == "🇺🇸"
+      assert Country.to_emoji("pl") == "🇵🇱"
+    end
+
+    test "converts subdivision codes" do
+      assert Country.to_emoji("GB-SCT") == "🏴󠁧󠁢󠁳󠁣󠁴󠁿"
+      assert Country.to_emoji("GB-WLS") == "🏴󠁧󠁢󠁷󠁬󠁳󠁿"
+      assert Country.to_emoji("GB-ENG") == "🏴󠁧󠁢󠁥󠁮󠁧󠁿"
+    end
+
+    test "maps GB-CYM to GB-WLS" do
+      assert Country.to_emoji("GB-CYM") == Country.to_emoji("GB-WLS")
+    end
+
+    test "converts alpha-3 codes" do
+      assert Country.to_emoji("USA") == "🇺🇸"
+      assert Country.to_emoji("GBR") == "🇬🇧"
+      assert Country.to_emoji("POL") == "🇵🇱"
+    end
+
+    test "converts IETF language tags" do
+      assert Country.to_emoji("en-US") == "🇺🇸"
+      assert Country.to_emoji("pl-PL") == "🇵🇱"
+    end
+
+    test "matches Flagmojis output for all alpha-2 codes" do
+      for %Flagmojis.Flag{iso: iso, emoji: expected} <- Flagmojis.Data.all() do
+        assert Country.to_emoji(iso) == expected,
+               "mismatch for #{iso}: expected #{expected}, got #{Country.to_emoji(iso)}"
+      end
+    end
+  end
+end