Update Bulgaria currency to EUR and deprecate BGN

Changed Bulgaria's currency from BGN to EUR in BulgariaCountryInfo. Marked BgnCurrency as obsolete, recommending the use of EurCurrency instead.

Author: tinohager

src/Nager.Country/CountryInfos/BulgariaCountryInfo.cs

@@ -45,7 +45,7 @@ public sealed class BulgariaCountryInfo : ICountryInfo
         ];
 
         /// <inheritdoc/>
-        public ICurrency[] Currencies => [new BgnCurrency()];
+        public ICurrency[] Currencies => [new EurCurrency()];
 
         /// <inheritdoc/>
         public string[] CallingCodes => ["359"];

src/Nager.Country/Currencies/BgnCurrency.cs

@@ -1,8 +1,11 @@
-namespace Nager.Country.Currencies
+using System;
+
+namespace Nager.Country.Currencies
 {
     /// <summary>
     /// Bgn Currency
     /// </summary>
+    [Obsolete("Replaced with ECurrency. Use EurCurrency instead.")]
     public sealed class BgnCurrency : ICurrency
     {
         /// <inheritdoc/>