Fix interpreter's incorrect downcast when an upcast is needed

[cyangle]

Fixes #16484

Gemini AI analysis of root cause and fix:

Root Cause

The interpreter's compile_call_arg method in compiler.cr was unconditionally calling downcast when casting an argument type to the target definition's argument type. This is incorrect because:

Downcast is for narrowing types (e.g., Union → String)
Upcast is for widening types (e.g., String → Union)
When calling arg_to_log(a) where a is a String but the method expects Int32 | String, the interpreter incorrectly tried to downcast String to Int32 | String, which failed because no such downcast handler exists (nor should it).

Fix

• Before blindly downcasting, check if an upcast is needed. If so, use upcast.
  

  crystal/src/compiler/crystal/semantic/bindings.cr

  Lines 489 to 493 in 07af861

  	if obj_type == filtered_type && !to_type.is_a?(GenericClassType) &&
  	to_type.can_be_stored?
  	filtered_type = to_type
  	@upcast = true
  	end

• Added a missing upcast_distinct handler for VirtualType → NonGenericClassType, which was exposed once the interpreter started using upcast in more places