feat(dmr): decode independent receiver slices

tests/dmr_bindings_test.pas

@@ -16,6 +16,10 @@ begin
     WriteLn(DMRLastError);
     Halt(1);
   end;
+  // Several simultaneous slice decoders share one dynamically loaded adapter.
+  if not DMRLoad then Halt(4);
+  DMRUnload;
+  if not DMRLoaded then Halt(5);
   Decoder := DMRMbeCreate(3);
   if Decoder = nil then Halt(2);
   try
@@ -27,5 +31,6 @@ begin
     DMRMbeDestroy(Decoder);
     DMRUnload;
   end;
+  if DMRLoaded then Halt(6);
   WriteLn('DMR native bindings tests passed');
 end.