Fix nullability annotations and localize strings

Co-authored-by: jeffkl <[email protected]>

Author: Copilot

src/NuGet.Core/NuGet.Protocol/Exceptions/QuotaExceededException.cs

@@ -1,6 +1,8 @@
 // Copyright (c) .NET Foundation. All rights reserved.
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
+#nullable enable
+
 using System;
 using System.Runtime.Serialization;
 

src/NuGet.Core/NuGet.Protocol/Resources/PackageUpdateResource.cs

@@ -546,8 +546,8 @@ await _httpSource.ProcessResponseAsync(
             {
                 TimeSpan? retryAfter = GetRetryAfter(response.Headers.RetryAfter);
                 string message = retryAfter.HasValue
-                    ? string.Format(CultureInfo.CurrentCulture, "Quota exceeded. Retry after {0} seconds.", retryAfter.Value.TotalSeconds)
-                    : "Quota exceeded. Retry after the time specified in the Retry-After header.";
+                    ? string.Format(CultureInfo.CurrentCulture, Strings.QuotaExceeded_RetryAfterSeconds, retryAfter.Value.TotalSeconds)
+                    : Strings.QuotaExceeded_RetryAfterHeader;
                 throw new QuotaExceededException(message, retryAfter);
             }
 

src/NuGet.Core/NuGet.Protocol/Strings.Designer.cs

@@ -539,4 +539,11 @@ The "s" should be localized to the abbreviation for seconds.</comment>
     <value>Invalid package id : `{0}`.</value>
     <comment>0 - package id.</comment>
   </data>
+  <data name="QuotaExceeded_RetryAfterSeconds" xml:space="preserve">
+    <value>Quota exceeded. Retry after {0} seconds.</value>
+    <comment>{0} - number of seconds to wait before retrying.</comment>
+  </data>
+  <data name="QuotaExceeded_RetryAfterHeader" xml:space="preserve">
+    <value>Quota exceeded. Retry after the time specified in the Retry-After header.</value>
+  </data>
 </root>