Skip encoder inspection on ToPython when no encoders registered

Extends the previous TryEncode optimization to the EncodableByUser gate in
Converter.ToPython. Previously every value conversion ran Type.GetTypeCode
plus enum/type checks before TryEncode could cheaply short-circuit on the
cached "no encoders" flag. EncodableByUser now checks HasEncoders first and
returns false immediately when none are registered (the common case), so the
entire encoder branch - including the type inspection - is skipped on the hot
per-value conversion path.

Also drop a redundant value.GetType() in EncodableByUser: the local already
holds value.GetType() at every call site, so compare against it directly.

Behavior is unchanged: with no encoders the branch was always going to fall
through; with encoders, HasEncoders is true so the gate reduces to the
previous EncodableByUser check.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: jhonabreul

src/runtime/Codecs/PyObjectConversions.cs

@@ -24,6 +24,12 @@ public static class PyObjectConversions
         // Set when an encoder is registered, cleared on Reset (shutdown).
         static volatile bool hasEncoders;
 
+        /// <summary>
+        /// True once at least one encoder has been registered. Lets hot conversion
+        /// paths skip encoder inspection entirely when none are registered.
+        /// </summary>
+        internal static bool HasEncoders => hasEncoders;
+
         /// <summary>
         /// Registers specified encoder (marshaller)
         /// <para>Python.NET will pick suitable encoder/decoder registered first</para>

src/runtime/Converter.cs

@@ -741,10 +741,19 @@ internal static bool ToManagedValue(BorrowedReference value, Type obType,
 
         static bool EncodableByUser(Type type, object value)
         {
+            // When no encoders are registered (the common case) skip the type
+            // inspection entirely: this runs on the hot per-value conversion path.
+            if (!PyObjectConversions.HasEncoders)
+            {
+                return false;
+            }
+
+            // type is already value.GetType() at every call site, so compare against
+            // it directly instead of calling GetType again.
             TypeCode typeCode = Type.GetTypeCode(type);
             return type.IsEnum
                    || typeCode is TypeCode.DateTime or TypeCode.Decimal
-                   || typeCode == TypeCode.Object && value.GetType() != typeof(object) && value is not Type;
+                   || typeCode == TypeCode.Object && type != typeof(object) && value is not Type;
         }
 
         static object? ToPyObjectSubclass(ConstructorInfo ctor, PyObject instance, bool setError)