Optimization: used StartsWith(char) instead of StartsWith(string) where supported

src/Serilog.Extensions.Logging/Extensions/Logging/SerilogLogger.cs

@@ -103,12 +103,12 @@ LogEvent PrepareWrite<TState>(LogEventLevel level, EventId eventId, TState state
                 {
                     messageTemplate = value;
                 }
-                else if (property.Key.StartsWith("@"))
+                else if (property.Key.StartsWith('@'))
                 {
                     if (_logger.BindProperty(GetKeyWithoutFirstSymbol(DestructureDictionary, property.Key), property.Value, true, out var destructured))
                         properties.Add(destructured);
                 }
-                else if (property.Key.StartsWith("$"))
+                else if (property.Key.StartsWith('$'))
                 {
                     if (_logger.BindProperty(GetKeyWithoutFirstSymbol(StringifyDictionary, property.Key), property.Value?.ToString(), true, out var stringified))
                         properties.Add(stringified);

src/Serilog.Extensions.Logging/Extensions/Logging/SerilogLoggerScope.cs

@@ -55,12 +55,12 @@ void AddProperty(string key, object? value)
         {
             var destructureObject = false;
 
-            if (key.StartsWith("@"))
+            if (key.StartsWith('@'))
             {
                 key = SerilogLogger.GetKeyWithoutFirstSymbol(SerilogLogger.DestructureDictionary, key);
                 destructureObject = true;
             }
-            else if (key.StartsWith("$"))
+            else if (key.StartsWith('$'))
             {
                 key = SerilogLogger.GetKeyWithoutFirstSymbol(SerilogLogger.StringifyDictionary, key);
                 value = value?.ToString();

src/Serilog.Extensions.Logging/Extensions/StringExtensions.cs

@@ -0,0 +1,14 @@
+using System.Runtime.CompilerServices;
+
+namespace Serilog.Extensions;
+
+#if !NET6_0_OR_GREATER && !NETSTANDARD2_1_OR_GREATER
+static class StringExtensions
+{
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public static bool StartsWith(this string str, char value)
+    {
+        return str.Length > 0 && str[0] == value;
+    }
+}
+#endif