Split message/proxy data up in MessageContext and ProxyMember

PluralKit.Core/Database/Functions/ProxyMember.cs

@@ -0,0 +1,17 @@
+#nullable enable
+using System.Collections.Generic;
+
+namespace PluralKit.Core
+{
+    /// <summary>
+    /// Model for the `proxy_members` PL/pgSQL function in `functions.sql`
+    /// </summary>
+    public class ProxyMember
+    {
+        public int Id { get; set; }
+        public IReadOnlyCollection<ProxyTag> ProxyTags { get; set; } = new ProxyTag[0];
+        public bool KeepProxy { get; set; }
+        public string ProxyName { get; set; } = "";
+        public string? ProxyAvatar { get; set; }
+    }
+}