fix(validation): reject server keys containing newlines

Use the strict \z end-of-string anchor for server key validation so keys
with a trailing newline cannot pass through the $ anchor.

Add regression cases for trailing LF, CRLF, and embedded newlines in
AsyncAPI 2.6.0 and 3.0.0. Escape carriage returns and newlines in
double-quoted YAML keys so the tests preserve these characters for
validation.

Author: VisualBean

src/ByteBard.AsyncAPI/Validation/Rules/AsyncApiDocumentRules.cs

@@ -16,7 +16,7 @@ public static class AsyncApiDocumentRules
         /// </summary>
         private static Regex keyRegex = new Regex(@"^[a-zA-Z0-9\.\-_]+$", RegexOptions.None, RegexTimeout);
 
-        private static Regex serverKeyRegex = new Regex(@"^[a-zA-Z0-9_\-]+$", RegexOptions.None, RegexTimeout);
+        private static Regex serverKeyRegex = new Regex(@"^[a-zA-Z0-9_\-]+\z", RegexOptions.None, RegexTimeout);
 
         public static ValidationRule<AsyncApiDocument> DocumentRequiredFields =>
             new ValidationRule<AsyncApiDocument>(

test/ByteBard.AsyncAPI.Tests/Validation/KeyRegexTests.cs

@@ -36,7 +36,7 @@ public static IEnumerable<TestCaseData> ServerKeys()
                 yield return new TestCaseData(version, key, true);
             }
 
-            foreach (var key in new[] { "server.one", "sérver", "server/name", "server name", "" })
+            foreach (var key in new[] { "server.one", "sérver", "server/name", "server name", "", "server\n", "server\r\n", "server\nother" })
             {
                 yield return new TestCaseData(version, key, false);
             }
@@ -63,6 +63,7 @@ public static IEnumerable<TestCaseData> ComponentKeys()
     public void ServerKey_UsesSpecificationPattern(string version, string key, bool valid)
     {
         var addressField = version == "2.6.0" ? "url" : "host";
+        var yamlKey = key.Replace("\r", "\\r").Replace("\n", "\\n");
         var input = $$"""
             asyncapi: {{version}}
             info:
@@ -71,7 +72,7 @@ public void ServerKey_UsesSpecificationPattern(string version, string key, bool
             channels:
               chat: {}
             servers:
-              '{{key}}':
+              "{{yamlKey}}":
                 {{addressField}}: localhost
                 protocol: kafka
             """;