Avoid some defensive copies on readonly structs in System.Net.Quic

src/libraries/System.Net.Quic/src/System/Net/Quic/Internal/MsQuicConfiguration.Cache.cs

@@ -2,11 +2,13 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 
 using System.Diagnostics;
+using System.Diagnostics.CodeAnalysis;
 using System.Collections.Generic;
 using System.Collections.Concurrent;
 using System.Collections.ObjectModel;
 using System.Security.Authentication;
 using System.Net.Security;
+using System.Runtime.InteropServices;
 using System.Security.Cryptography.X509Certificates;
 using System.Threading;
 using Microsoft.Quic;
@@ -47,6 +49,8 @@ private static bool GetConfigurationCacheEnabled()
         public readonly List<SslApplicationProtocol> ApplicationProtocols;
         public readonly QUIC_ALLOWED_CIPHER_SUITE_FLAGS AllowedCipherSuites;
 
+        [UnscopedRef] private readonly ReadOnlySpan<byte> SettingsSpan => MemoryMarshal.AsBytes(new ReadOnlySpan<QUIC_SETTINGS>(in Settings));
+
         public CacheKey(QUIC_SETTINGS settings, QUIC_CREDENTIAL_FLAGS flags, X509Certificate? certificate, ReadOnlyCollection<X509Certificate2>? intermediates, List<SslApplicationProtocol> alpnProtocols, QUIC_ALLOWED_CIPHER_SUITE_FLAGS allowedCipherSuites)
         {
             CertificateThumbprints = certificate == null ? new List<byte[]>() : new List<byte[]> { certificate.GetCertHash() };
@@ -98,7 +102,7 @@ public bool Equals(CacheKey other)
 
             return
                 Flags == other.Flags &&
-                Settings.Equals(other.Settings) &&
+                SettingsSpan.SequenceEqual(other.SettingsSpan) &&
                 AllowedCipherSuites == other.AllowedCipherSuites;
         }
 

src/libraries/System.Net.Quic/src/System/Net/Quic/Internal/MsQuicSafeHandle.cs

@@ -88,7 +88,7 @@ internal sealed class MsQuicContextSafeHandle : MsQuicSafeHandle
     /// Holds a weak reference to the managed instance.
     /// It allows delegating MsQuic events to the managed object while it still can be collected and finalized.
     /// </summary>
-    private readonly GCHandle _context;
+    private GCHandle _context;
 
     /// <summary>
     /// Optional parent safe handle, used to increment/decrement reference count with the lifetime of this instance.

src/libraries/System.Net.Quic/src/System/Net/Quic/Internal/ReceiveBuffers.cs

@@ -52,7 +52,7 @@ public int CopyFrom(ReadOnlySpan<QUIC_BUFFER> quicBuffers, int totalLength, bool
             int totalCopied = 0;
             for (int i = 0; i < quicBuffers.Length; ++i)
             {
-                Span<byte> quicBuffer = quicBuffers[i].Span;
+                ReadOnlySpan<byte> quicBuffer = quicBuffers[i].Span;
                 if (totalLength < quicBuffer.Length)
                 {
                     quicBuffer = quicBuffer.Slice(0, totalLength);

src/libraries/System.Net.Quic/src/System/Net/Quic/Interop/msquic.cs

@@ -20,7 +20,7 @@ namespace Microsoft.Quic
 {
     internal unsafe partial struct QUIC_BUFFER
     {
-        public Span<byte> Span => new(Buffer, (int)Length);
+        public readonly Span<byte> Span => new(Buffer, (int)Length);
     }
 
     internal partial class MsQuic